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GNU Anubis Manual

Copyright (C) 2001, 2002, 2003, 2004 Wojciech Polak and Sergey Poznyakoff.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover texts being "A GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License".

(a) The FSF's Back-Cover Text is: "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development."

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1. GNU Anubis

This edition of the GNU Anubis Manual, last updated 18 December 2004, documents GNU Anubis Version 4.0.

2. Overview  Preliminary information.
3. Glossary of Frequently Used Terms  Frequently Used Terms Explained.
4. Authentication  How Incoming Connections Are Authenticated.
5. Configuration  Writing your own configuration files.
6. The Rule System  How to use the Rule System.
7. Invoking GNU Anubis  How to invoke the GNU anubis.
8. Sample Beginning  Here is a sample beginning.
9. Using the TLS/SSL Encryption  
10. Using S/MIME Signatures  Using S/MIME signatures.
11. Using Mutt with Anubis  Using Anubis with Mutt.
12. Reporting Bugs  Reporting bugs.


13. Pixie & Dixie  Original description of the new GNU Anubis operation mode.
A. GNU Free Documentation License  This manual is under the GNU Free Documentation License.

Concept Index  Index of concepts.

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2. Overview

GNU Anubis is an SMTP message submission daemon. Its purpose is to receive the outgoing message, perform some manipulations over its contents, and to forward the altered message to the mail transport agent.

The usual mail sending scheme looks as follows: the user composes his message using mail user agent (MUA for short). Once the message is composed, the user sends it. When the MUA receives the send command it connects to the mail transport agent (MTA for short) and passes it the message for delivery. The figure below illustrates this interaction:

+-------+                 +-------+               
|  MUA  | ---[outmsg]---> |  MTA  | ... [outmsg]
+-------+                 +-------+         |     
                                     |  Recipient's |
                                     |   Mailbox    |  

As shown in this figure, the outgoing message (outmsg), reaches the recipient's mailbox unaltered.

However, there are situations where it may be necessary to modify the outgoing message before it reaches MTA. As the simplest example, the user might wish to sign the outgoing messages with his PGP key, but his MUA does not support this operation or supports it unconditionally.

In such cases, installing GNU Anubis between the MUA and MTA allows the user to perform any additional processing on the sent message. The figure below illustrates this concept:

+-------+                 +--------+                 +-------+               
|  MUA  | ---[outmsg]---> | Anubis | ---[modmsg]---> |  MTA  | 
+-------+                 +--------+                 +-------+     
                                                  |  Recipient's |
                                                  |   Mailbox    |  

The outgoing message is processed by GNU Anubis, and it is the resulting message (modmsg) that reaches the MTA.

GNU Anubis is able to perform on messages a wide set of operations, such as modifying message headers or body, encrypting or signing messages with GPG (GNU Privacy Guard) keys, installing secure tunnels to MTA using TLS/SSL encryption, tunneling messages through SOCKS proxies, etc.

When the set of built-in operations is not enough, the user can define his own operations using Guile, a GNU's Ubiquitous Intelligent Language for Extensions.

The message processing is controlled by system-wide and per-user configuration files written in a flexible and easy to use command scripting language, specially designed for this purpose.

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3. Glossary of Frequently Used Terms

A process whereby Anubis determines the authenticity of the connecting party, its user name and configuration settings.

Any standard for the exchange of information. A protocol defines the specific wording and control flow for communications between two or more programs, devices, or systems.

Simple Mail Transport Protocol is a common mechanism for exchanging mail across a network. This protocol is described in the RFC 821 document.

We use a term daemon to define a process that runs in the background, doing automated processing.

A server provides information or other services for its clients. Most network protocols are client--server based. This term usually refers to an entire machine, but it can refer (and we're doing that) also to the particular program or process, on that machine, that provides the service.

We use a term proxy to define a program, which goes between the MUA and the MTA (it makes a tunnel). It can be used as a gateway to the outside world, while using a firewall. In this case the host under the firewall sends data to the proxy server, which in turn forwards it to the real server outside, receives the response, and passes it back to the internal host.

GNU's Ubiquitous Intelligent Language for Extensions. It provides a Scheme interpreter conforming to the R4RS language specification. GNU Anubis uses Guile as its extension language. For more information about Guile, See section `Overview' in The Guile Reference Manual.

GNU Privacy Guard, a tool compatible with the Pretty Good Privacy.

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4. Authentication

When GNU Anubis accepts an incoming connection, it first has to identify the remote party, i.e. determine whether it has the right to use Anubis resources and, if so, what configuration settings should be used during the session. We call this process authentication. The exact method of authentication depends on Anubis operation mode. Currently there are two modes:

This is the default mode. It is compatible with versions of GNU Anubis up to 3.6.2. In this mode, Anubis relies on AUTH service (identd) to authenticate users.

This mode uses SMTP AUTH mechanism to authenticate incoming connections. See section 13. Pixie & Dixie, this is the first draft description of this mode.

Both modes have their advantages and deficiencies, which you have to weigh carefully before choosing which one to use. These are discussed below:

Transparent (`traditional') mode.


  1. The user must have identd installed on his machine.
  2. Each user must have a system account on the machine where GNU Anubis runs (though the system administrator may relax this limitation using user name translation, see section 5.3 TRANSLATION Section).


  1. Relative simplicity. You don't have to create your users database.
  2. Authentication is performed immediately after the connection.

Auth mode.


  1. You have to maintain your users database
  2. User's MUA must be able to perform ESMTP AUTH.(1)


  1. Better reliability.
  2. Users do not have to run identd on their machines.
  3. Users are not required to have accounts on the machine where Anubis runs.
  4. Users can remotely modify their configuration files.

4.1 User Database  
4.2 Database URL  
4.3 Managing the Database  

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4.1 User Database

GNU Anubis uses User Database for keeping user credentials, i.e. data used to authenticate and authorize users. The exact way of storing these data does not matter here, it will be addressed further in this manual. In this section we treat user database as an abstraction layer.

The user database consists of records. Each record keeps information about a particular user. A record consists of four fields. A field may contain some value, or be empty, in which case we say that the field has null value.

The record fields are:

SMTP authentication ID of the user.

SMTP password.

System user name to be used.

Path to the configuration file.

The first two fields are mandatory and must always have non-null values. No two records in the database may have the same value of SMTP AUTHID field. When anubis is trying to authenticate a user, it first looks up in the database a record with the value of SMTP AUTHID field matching AUTHID given by the user. If no such entry is found, authentication fails. Otherwise, anubis goes on and compares the password supplied by the user with that from AUTH PASSWORD column. If these match, authentication succeeds and anubis passes to authorization state.

In this state, it first determines the user ID (UID) to switch to. If the ACCOUNT field is not null, its value is used as a login name of the system account to use. If it is null, anubis switches to the privilege level of a default not privileged user, specified by user-notprivileged statement in the global configuration file (see section user-notprivileged).

The final step is to parse user configuration file. If CONFIG field is not null, its value is used as absolute path to the configuration file. Otherwise, anubis searches for file `~/.anubisrc' (where `~' denotes home directory for the system account obtained on the previous step) and if such a file exists, loads it.

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4.2 Database URL

Anubis database is identified by its URL, or Universal Resource Locator. A URL consists of following elements (square brackets enclose optional elements):


The detailed description of each URL part follows:

Specifies a database protocol. The protocol describes how the database is to be accessed. In a way, it may be regarded as specifying the database type. Currently, GNU Anubis supports following database protocols:

`text' A plain text file, containing users' credentials.
`gdbm' GDBM database
`mysql' MySQL database
`pgsql' PostgreSQL database
`postgres' Alias for `pgsql'.

These protocols are described in detail below.

User name necessary to access the database.

User password necessary to access the database.

Domain name or IP address of a machine running the database.

A path to the database. The exact meaning of this element depends on the database protocol. It is described in detail when discussing particular database protocols.

A list of protocol-dependent parameters. Each parameter is of the form keyword=name, parameters are separated by semicolons.

4.2.1 Plain text databases  
4.2.2 Databases in GDBM format  
4.2.3 MySQL and PostgreSQL  MySQL and PostgreSQL databases

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4.2.1 Plain text databases

This is the simplest database possible. It is kept in a plain text file. Each line in this file represents a single record, empty lines and lines beginning with `#' (comments) sign are ignored. Records consist of fields, each field being a sequence of characters. Fields are separated by colons (`:', ASCII 58). If `:' character occurs in a field, it is preceeded by a single backslash character (`\\', ASCII 92). A record must contain at least two fields.

  2. SMTP password.
  3. Account name.
  4. Path to user configuration file.

URL syntax

The URL syntax for this type of databases is quite simple:


where path specifies absolute file name of the database file.

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4.2.2 Databases in GDBM format

The protocol value `gdbm' specifies a GDBM database. For the detailed description of GDBM system section `Introduction' in The GNU DBM Manual.

URL syntax for GDBM databases is:


where path specifies absolute file name of the database file.

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4.2.3 MySQL and PostgreSQL

This is the most flexible database format. GNU Anubis 4.0 supports MySQL(2) and PostgreSQL(3) interfaces. No matter which of them you use, the implementation details are hidden behind a single consistent Anubis interface.

GNU Anubis supposes that all user data are kept in a single database table. This table must have at least four columns for storing SMTP `AUTHID', SMTP password, system account name and path to user configuration file. Among those, only the last two may have NULL values. There is no restriction on the name of the database or the authentication table, nor on its column names. This information may be specified in URL as discussed below.

URL syntax


Proto describes the exact database type to use. Use `mysql' for MySQL databases and `pgsql' or `postgres' for PostgreSQL databases.

Optional user and password specify authentication credentials used to access the database.

Host sets domain name or IP address of the machine running the database. It may be omitted if the database resides on `localhost'.

The database name is specified by dbname element.

Finally, further details needed for connecting to the database may be given by URL parameters. All of them have reasonable default values, so you'll have to specify only those parameters that does not match the default values. Known parameters are:

Specifies the port number to be used when connecting to the database. If it is not specified, the behavior depends on the value of socket parameter: if socket is not present, the program will use the default port number for the given protocol (i.e. 3306 for `mysql' and 5432 for `pgsql'.

Specifies UNIX name of the socket to connect to. This parameter cannot be used together with port (see above).

Sets the length of the buffer used to create SQL queries. Default is 1024 bytes.

Specifies the name of database table keeping where the authentication data are stored. Default is `users'.

Specifies the name of a column in table which holds `AUTHID' value. Default is `authid'.

Specifies the name of a column in table which holds user password. Default is `passwd'.

Specifies the name of a column in table which holds the name of system account to be used for this `AUTHID'. Default is `account'.

Specifies the name of a column in table which holds path to the user's configuration file. Default is `rcfile'.

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4.3 Managing the Database

Managing the user database is a complex task, which looks differently from administrator's and user's point of view. The administrator have full rights on the database, it can add new records and delete or modify existing ones. A user, of course, does not have such ample rights. The only thing he is able to do is to maintain his own record in the database, provided that he already has one. If he does not, he should contact the system administrator and arrange for the creation of his record.

4.3.1 Administrators  The Administrator's View
4.3.2 Users  The User's View

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4.3.1 Administrators

All administrative tasks are done using anubisadm command --- a multipurpose tool for Anubis administrator.

The command usage syntax is:

anubisadm command [options] database-url

where command specifies the operation to be performed on the database, options give additional operation-specific parameters, and database-url specifies the database to operate upon.

All administrative tasks can be subdivided into the following five categories:

These operations are described in detail in the following subsections . Creating the Database Listing Database Records Adding New Records Removing Existing Records Modifying Existing Records Summary of All Administrative Commands  

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To create a database use anubisadm --create (or anubisadm -c) command. Anubisadm will read database entries from the standard input and write them to the database. The standard input is supposed to be formatted as text database (see section 4.2.1 Plain text databases).

Thus to create a GDBM database from plain text file `userlist', use the following command

anubisadm --create gdbm:/etc/anubis.db < userlist

Similarly, to create an initially empty database, type

anubisadm --create gdbm:/etc/anubis.db < /dev/null

Notice, that if you use SQL database format, `--create' command does not imply creating the database structure! So, before running

anubisadm --create mysql://localhost/dbname < userlist

make sure you create the underlying database structure (including granting privileges to the anubis user), via the usual procedure. Please refer to corresponding database manual for the detailed instructions on this.

It is sometimes necessary to convert the existing user database from one format (protocol) to another. For example, suppose you have been running GDBM database (text:/etc/anubis.db) for some time, but now it has grown considerably and you decided to switch to PostgreSQL database to improve performance. To do so, first create the database using postgres utilities. Then run

anubisadm --list text:/etc/anubis.db | \
 anubisadm --create pgsql://localhost/dbname

That's all there is to it!

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The command `--list' (or `-l') lists the existing database. When run without additional options, it will display all records from the database, e.g.:

anubisadm --list gdbm:/etc/anubis.db

Among its other uses, such invocation is handy for converting user database to another format (see section Creating the Database).

If you wish to list only a particular record, specify the AUTHID using `--authid' (`-i') option. For example, to list record of the user with AUTHID `test', type:

example$ anubisadm --list --authid test gdbm:/etc/anubis.db

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To add a new record use command `--add' (`-a'). Additional data are specified via the following options:

`-i string'
Specify the user SMTP AUTHID.

`-p string'
Specify user password password.

`-u string'
Specify system user name corresponding to the given AUTHID.

`-f string'
Specify configuration file to be used for this user.

For example, the following command adds a record with SMTP AUTHID `test', password `guessme' and maps it to the system account `gray':

anubisadm --add --authid test --password guessme \
          --user gray gdbm:/etc/anubis.db

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Removing a record is quite straightforward: use `--remove' (`-r') command and specify AUTHID using `--authid' option. For example, to remove the record created in the previous subsection, run:

anubisadm --remove --authid test gdbm:/etc/anubis.db

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To modify an existing record use command `--modify' (`-m'). The record is identified via `--authid' option. The fields to be changed are given with the following options:

`-p string'
Specify user password password.

`-u string'
Specify system user name corresponding to the given AUTHID.

`-f string'
Specify configuration file to be used for this user.

For example, the following command sets new configuration file name for the user `smith':

anubisadm --authid smith \
          --rcfile=/var/spool/anubis/common gdbm:/etc/anubis.db

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anubisadm command [options] database-url


Create the database.

List the contents of an existing database.

Add a new record.

Modify an existing record.

Remove an existing record.

Display program version number and exit.

Display short usage summary and exit.


`-i string'
Specify the authid to operate upon. This option is mandatory for `--add', `--modify' and `--remove' commands. It may also be used with `--list' command.

`-p string'
Specify the password for the authid. This option is mandatory for `--add', `--modify' and `--remove' commands.

`-u string'
Specify the system user name corresponding to the given authid. It may be used with `--add', `--modify', and `--remove' commands.

`-f string'
Specify the rc file to be used for this authid. The option may be used with `--add', `--modify', and `--remove' commands.

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4.3.2 Users

Users maintain their database records using anubisusr command. Main purpose of this command is to keep the copy of your configuration on GNU Anubis server up to date. . We recommend to invoke anubisusr from your `~/.profile', which will make sure that your configuration file is up to date when you log in. (4).


anubisusr [options] [smtp-url]

where smtp-url is a URL of your GNU Anubis server. Notice that if it lacks user name and password, then anubisusr will first try to retrieve them from your `~/.netrc' file (See netrc(5) for more info), and if not found it will prompt you to supply them.


`-m mech'
`--mechanism mech'
Only use SASL mechanism mech. Use this option several times to set a list of allowed mechanisms.

Verbose output. Multiple options increase the verbosity. Maximum verbosity level is 3.

Display program version number and exit.

Display short usage summary and exit.

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5. Configuration

The behavior of GNU Anubis is controlled by two configuration files. The system configuration file, `/etc/anubisrc', specifies system-wide options that affect all users. This file is usually owned by root. The user configuration file specifies what GNU Anubis should do for a particular user. By default it is located in `~/.anubisrc'. This location can be changed in auth mode. To protect your passwords in the configuration files, use the 0600 (u=rw,g=,o=) permissions, otherwise GNU Anubis won't accept them.

Lexical Structure

Both configuration files use simple line-oriented syntax. Each line introduces a single statement. A statement consists of words, each word being defined as a contiguous sequence of non-whitespace symbols. A word may be composed of alphanumeric characters and any of the following punctuation symbols: `_', `.', `/', `-'. Any arbitrary sequence of characters enclosed in a pair of double quotes is also recognized as a word.

The familiar shell here document syntax may be used to produce a word containing several lines of text. The syntax is:


If "here document" starts with `<<-', then all leading tab characters are stripped from input lines and the line containing delimiter. This allows to indent here-document in a natural fashion.

To summarize all the above, let's consider the example:

first-word "second word" <<-EOT
                            Third word
                            containing several
                            lines of text

This line contains three words: `first-word', `second word' and the third one composed of the three lines between the `EOT' markers.

If a statement is very long, it may be split among several lines of text. To do so, precede the newline characters with a backslash `\', e.g.:

a very long statement\
  occupying several lines\
  of text

A `#' in a line starts a comment. It and the rest of the line are ignored. Comments may appear on any of the lines in the configuration file, except on a commands and within a "here-document" construction. A line containing just a comment (with perhaps spaces before it) is effectively blank, and is ignored. For example:

# This is a comment
if header[Subject] :re "No.*"  # This is also a comment
  guile-process action-name This # is not a comment!!!

Logical Structure

The statements within a configuration file are grouped into sections. Each section has its name. A section begins with one of the following constructs:

BEGIN name
---BEGIN name---

and ends with one of the following constructs:


Notice, that both `BEGIN' and `END' must be uppercase. When using the second form, any amount of whitespace is allowed between the three dashes and the word.

The sections cannot be nested.

There are five predefined sections, whose names are uppercase. The user may define his own sections, which may then be referred to from the RULE section as subroutines (see section 6.6.2 Call Action).

The predefined section names are:

Controls authentication mechanisms.
This section specifies the basic GNU Anubis behavior. Its presence is required in the system configuration file. It may be used in the user configuration file to override the system-wide settings.
This section specifies a translation map for remapping remote or local users. It may be used only in the system-wide configuration file.
Contains the settings of the Guile interpreter. The section is allowed in both configuration files.
Defines the rules that are used to alter the contents of the messages (conditional and unconditional rules).

5.1 AUTH Section  
5.2 CONTROL Section  
5.3 TRANSLATION Section  
5.4 GUILE Section  

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5.1 AUTH Section

AUTH session controls various aspects of authentication mode.

Option: smtp-greeting-message text
Configures the greeting message issued by GNU Anubis upon accepting the connection.

Option: smtp-help-message help-text
Sets the test of the message issued by Anubis in response to SMTP HELP command. Help-text is a list of strings. Each string from the list will be displayed at a separate response line.

Option: sasl-password-db url
Sets the user database URL (see section 4.1 User Database).

Option: sasl-allowed-mech mech-list
Defines the list of allowed authentication methods.

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5.2 CONTROL Section

The `CONTROL' section specifies the basic GNU Anubis behavior. Specified in the system configuration file, it applies to all users on the machine, but each user can specify its own `CONTROL' section, to customize own settings. Of course, not all options can be set or change by user. Some options can only be set in the system configuration file, and some only in user configuration file. By default, options specified in user configuration file have a higher priority that those specified in system configuration file.

All option names are case insensitive, so you can use for instance: bind or BIND or BiNd, and so on.

5.2.1 Basic Settings  
5.2.2 Output Settings  
5.2.3 Proxy Settings  
5.2.4 ESMTP Authentication Settings  
5.2.5 Encryption Settings  
5.2.6 Security Settings  

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5.2.1 Basic Settings

Option: bind [host:]port
Specify the TCP port on which GNU Anubis listens for connections. The default host value is `INADDR_ANY', which means that anyone can connect to GNU Anubis. The default port number is 24 (private mail system). This option is available only in the system configuration file. If you would like, for instance, to bind GNU Anubis to port 25 (SMTP) and limit its clients only to those from `localhost', then set the following in your system configuration file:

bind localhost:25

Option: remote-mta host[:port]
Specify a remote SMTP host name or IP address, which GNU Anubis will connect and forward mail to (after a processing). The default port number is 25. This option is available in both configuration files.

Option: local-mta file-name [args]
Execute a local SMTP server, which works on standard input and output (inetd-type program). This option excludes the `remote-mta' keyword (or `--remote-mta' command line option). For example:

local-mta /usr/sbin/sendmail -bs

Option: mode mode-name

Selects Anubis operation mode. Allowed values for mode-name are:


See section 4. Authentication, for the detailed discussion of GNU Anubis operation modes.

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5.2.2 Output Settings

Option: termlevel level
This is a logging level for syslogd or a terminal (if using the `--foreground' command line option). level can be one of the following:

Only errors are logged. This is the default level.

Produce more diagnostic output.

Produce debugging output.

Do not log anything.

This command may be used only in system configuration file.

Option: logfile file-name
This command specifies an additional file, where GNU Anubis can log its information, but only those information available for a client. Only in user configuration file. For example:

logfile "anubis.log"

This will log to the `~/anubis.log' file in a client's home directory.

Option: loglevel level
This option specifies an output level for an additional file (`logfile'). It can be used only in user configuration file. level is one of the following:


Option: tracefile yes-or-no
Option: tracefile file-name
This option instructs anubis to log the execution of tests and actions from the RULE sections. This is useful for debugging the configuration files.

When this option is used in the system-wide configuration file, only its first form is allowed. Using `tracefile yes' enables logging of the actions and tests to the default syslog channel. Using `tracefile no' disables it.

When used in the user configuration file, a filename is allowed as an argument to this option. This allows you to explicitly specify to which file the tracing output should go. Otherwise, using `tracefile yes' enables logging to the same file as `logfile' (if possible).

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5.2.3 Proxy Settings

Option: socks-proxy host[:port]
This option enables tunneling the connections through a SOCKS proxy server, specified as an argument host. The port default value is 1080, which is a common port number for SOCKS proxies.

Option: socks-v4 yes-or-no
This specifies a SOCKS protocol version 4. By default it is turned off, and a default mode is SOCKS protocol version 5.

Option: socks-auth username:password
Specify a user name and a password, if a SOCKS proxy server requires them. A username and a password are separated with a colon (`:').

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5.2.4 ESMTP Authentication Settings

The following options set authentication credentials for ESMTP authentication. You may use this option, for example, if your MTA requires such an authentication, but your MUA does not support it.

Option: esmtp-allowed-mech mech-list
Defines the list of allowed authentication mechanisms. Mech-list is a list of valid authentication mechanism names separated by whitespace.

Anubis selects the authentication method using following algorithm: The MTA presents the list of authentication methods it supports. For each element in mech-list, Anubis tests whether it is available in the list presented by MTA. If found, this method is selected. For example, suppose that the MTA supports following mechanisms:


and you have following statement in your configuration file

esmtp-allowed-mech DIGEST-MD5 CRAM-MD5 LOGIN

In this case Anubis will select CRAM-MD5.

Option: esmtp-require-encryption mech-list
This statement declares the list of mechanisms that can be used only over a TLS encrypted channel. By default Anubis uses

esmtp-require-encryption LOGIN PLAIN

This prevents sending user password over an unencrypted connection.

Option: esmtp-auth-id authentication-id
Sets authentication ID (user name).

Option: esmtp-authz-id authorization-id
Sets authorization ID (user name).

Option: esmtp-password password
Sets password to be used in authentication.

Option: esmtp-auth username:password
This option sets both authentication and authorization IDs and the password. It is equivalent to

esmtp-auth-id username
esmtp-authz-id username
esmtp-password password

The following options specify authentication credentials for GSSAPI, DIGEST-MD5 and KERBEROS_V5 authentication mechanisms:

Option: esmtp-service service-name
Sets the name of GSSAPI service.

Option: esmtp-hostname hostname
Sets hostname of the machine.

Option: esmtp-generic-service servise-name
Sets generic service name.

Option: esmtp-passcode passcode
Sets passcode.

Option: esmtp-realm realm-name
Sets GSSAPI realm.

Following option is useful with ANONYMOUS authentication mechanism:

Option: esmtp-anonymous-token token
Sets the token to be used with ANONYMOUS authentication mechanism

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5.2.5 Encryption Settings

Option: ssl yes-or-no
This option enables the TLS/SSL encryption between the MUA and the MTA. Value `no' is the default, but using the TLS/SSL encryption is recommended. You should also specify a private key and a certificate using the `ssl-key' and `ssl-cert' keywords (defined below). See section 9. Using the TLS/SSL Encryption, for details.

Option: ssl-oneway yes-or-no
This option enables the ONEWAY encryption. Use this mode, when you want to use the TLS/SSL, but your MUA doesn't provide a support for ESMTP TLS/SSL. Using this option doesn't require using the `ssl-key' and `ssl-cert' keywords.

Option: ssl-cert file-name
Specify a certificate for the TLS/SSL encryption. Value `anubis.pem' is the default.

Option: ssl-key file-name
Specify a private key for the TLS/SSL encryption. Value `anubis.pem' is the default.

Option: ssl-cafile file-name
Specify a CA certificate file (supported only by GnuTLS).

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5.2.6 Security Settings

The following options control various security settings.

Option: allow-local-mta yes-or-no
For security reasons, this option is set to `no', but the `yes' value enables the `local-mta' keyword (or `--local-mta' command line option), so if you want to use a local mail server, which works on standard input and output, a supervisor must set this option to `yes'. The option is available only in system configuration file.

Option: drop-unknown-user yes-or-no
This option drops an unknown user, i.e. a client which has not been verified by IDENT service. Value `no' is the default.

Option: user-notprivileged username
For security reasons, it is recommended to create an unprivileged user, which the server runs as most of the time, when doing unprivileged operations. The option is available only in system configuration file. For example:

user-notprivileged "anubis.unprivileged"

Caution: Create a user account named `anubis.unprivileged' in the `/etc/passwd', if necessary. Add this user name also to the `/etc/anubis.allow', if using GNU Anubis with PAM support.

Option: rule-priority value

This statement defines the order of execution of the system and user RULE sections (See section 6. The Rule System, for detailed description). It is available only in system configuration file.

The system section is executed first, then the user section is executed.

The user section is executed first, next the system section is executed.

Only the system RULE section is executed.

Only the user RULE section is executed.

Option: control-priority value

Sets the order of processing the CONTROL sections. The option is available only in system configuration file. Its possible values are:

The system CONTROL section is processed first. Notice, that this means that the user may override the system settings in his configuration file. This is the default setting.

The user CONTROL section is processed first. Thus, the system-wide settings always override the user private settings.

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The `TRANSLATION' section specifies how to translate remote or local user names, or host names or addresses, to local user names. The `TRANSLATION' section is available only in the system configuration file. Syntax:

translate  [user@]address into  username

address means host name or IP address. You can also specify `', and it means any address (`INADDR_ANY').

An example:

translate jack@somewhere.net into john

The rule above will allow a remote user `jack' at `somewhere.net' to use the configuration file of the local user `john'. Or you can write: `translate somewhere.net into john', and this means that all users at `somewhere.net' are allowed to use the local john's configuration file.

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5.4 GUILE Section

Command: guile-output file
Specifies the name of the file to bind to the Scheme standard error and output ports. This option has no effect if GNU Anubis is started with either of `--foreground' or `--stdio' command line options.

Command: guile-debug yes-or-no
When set to `yes' enables Guile stack traces and debugging output.

Command: guile-load-path-append path
Appends the given path to the list of Guile load paths (see section `Build Config' in The Guile Reference Manual).

Command: guile-load-program file
Reads the given Scheme program.

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6. The Rule System

The rule system is a core part of GNU Anubis. It can be regarded as a program that is executed for every outgoing message.

Throughout this chapter, when showing syntax definitions, the optional parts of these will be enclosed in a pair of square brackets, e.g.:

keyword [optional-part] mandatory-part

When the square braces are required symbols, they will be marked as such, e.g.:

remove `['key`]'

The rule system is defined in RULE section. The statements within this section are executed sequentially. Each statement is either an action or a conditional statement.

6.1 Actions  
6.2 Conditional Statements  
6.3 Triggers  
6.4 Boolean Operators  
6.5 Regular Expressions  
6.6 Action List  
6.7 Using Guile Actions  

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6.1 Actions

An action is a statement defining an operation to be performed over the message. Syntactically, each action is

command [=] right-hand-side

Where command specifies a particular operation and right-hand-side specifies the arguments for it. The equal sign is optional.

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6.2 Conditional Statements

A conditional statement defines the control flow in the section. It allows to execute arbitrary actions depending on whether a certain condition is met. A conditional statement in its simplest form is:

if part [pattern-match-flags] cond-expr
The part specifies which part of the input should be considered when evaluating the condition. It is either `command', meaning the text of an smtp command issued while sending the message, or `header', meaning the value of an RFC822 header. Either of the two may be followed by the name of the corresponding command or header enclosed in square brackets. If this part is missing, all command or headers will be searched.

The optional pattern-match-flags alter the pattern matching type used in subsequent conditional expression. It will be described in detail in the section 6.5 Regular Expressions. The cond-expr is a conditional expression. It consists of a series of conditions joined together with boolean operators `and' or `or' (see section 6.4 Boolean Operators). Each condition is:

= regexp
Returns true if the requested part of the input matches the given regular expression (regexp).

!= regexp
Returns true if the requested part of the input does not match the given regular expression.

not condition
Reverses the sense of condition

( cond-expr )
Returns the result of the conditional expression in parentheses. This is useful for changing operator precedence.

The simplest example:

if header [Subject] "^ *Re:"

The actions represented by ... will be executed only if the `Subject:' header of the message starts with `Re:' optionally preceded by any amount of whitespace.

The more elaborate form of a conditional allows you to choose among the two different action sets depending on a given condition. The syntax is:

if part [flags] cond-expr

Here, the action-list-1 is executed if the condition cond-expr is met. Otherwise, action-list-2 is executed.

if part [flags] cond-expr

Note also, that in the examples above any of the statements action-list may contain conditionals, so that the conditional statements may be nested. This allows to create very sophisticated rule sets. As an example, consider the following statement:

if [List-Id] :re ".*"
  modify [Subject] "[Anubis Commit Notice] &"
  if [List-Id] :re ".*"
    modify [Subject] "[Anubis Bug Notice] &"
    add [X-Passed] "Subject checking"

This statement, depending on the value of List-Id header, will prepend the Subject header with an identification string, or add an X-Passed header if no known List-Id was found.

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6.3 Triggers

Triggers are conditional statements that use the value of the `Subject' header to alter the control flow. Syntactically, a trigger is:

trigger [flags] pattern

Here, pattern is the pattern against which the `Subject' header is checked, flags are optional flags controlling the type of regular expression used (see section 6.5 Regular Expressions). For backward compatibility, the keyword rule may be used instead of trigger.

The triggers act as follows: First, the value of the `Subject' header is matched against the pattern `@@'pattern. If it matches, then the matched part is removed from the `Subject', and the action-list is executed.

Basically, putting aside the possibility to use different flavors of regular expressions, a trigger is equivalent to the following statement:

if header[Subject] :posix "(.*)@@pattern"
  modify header [Subject] "\1"

Thus, adding the `@@rule-name' code to the `Subject' header of your message, triggers a rule named rule-name, specified in a user configuration file. For example:

trigger :basic "^gpg-encrypt-john"
   gpg-encrypt "john's_gpg_key"

Now you can simply send an email with the following subject: `hello John!@@gpg-encrypt-john' to process an outgoing message with the rule specified above--encrypt message with a John's public key. Moreover, the trigger will remove the `@@', so John will only receive a message with a subject `hello John!'.

Another example shows an even more dynamic trigger, that is using a substitution and back-references:

trigger :extended "^gpg-encrypt:(.*)"
   gpg-encrypt "\1"
   add [X-GPG-Comment] "Encrypted for \1"

To encrypt a message to user e.g. `John', simply send an email with a subject `hello John!@@gpg-encrypt:john's_gpg_key'. This way, you decide at a run time which public key should be used, without creating separate rules for each user; thanks to back-references, those 3--4 lines are enough.

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6.4 Boolean Operators

The following table lists the three boolean operators that can be used in Anubis conditional expressions in the order of increasing binding strength:

As an example, let's consider the following statement:

if header[X-Mailer] "mutt" or header[X-Mailer] "mail" \
   and not header[Content-Type] "^multipart/mixed;.*"

In this case the action will be executed if the X-Mailer header contains the word `mutt'. The same action will also be executed if the X-Mailer header contains the word `mail' and the value of the Content-Type header does not begin with the string `multipart/mixed'.

Now, if we wished to execute the action for any message sent using mail or mutt whose Content-Type header does not begin with the string `multipart/mixed', we would write the following:

if (header[X-Mailer] "mutt" or header[X-Mailer] "mail") \
   and not header[Content-Type] "^multipart/mixed;.*"

Notice the use of parentheses to change the binding strength of the boolean operators.

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6.5 Regular Expressions

GNU Anubis supports two types of regular expressions: POSIX (both basic and extended), and Perl-style regular expressions. Among this, the former are always supported, whereas the support for the latter depends on the configuration settings at compile time. The default type of regular expressions is POSIX Extended.

A number of modifiers is provided to change the type of regular expressions. These are described in the following table.

Indicates that the following pattern should be considered a regular expression. The default type for this expression is assumed.

The regular expression is a Perl-style one.

Disables regular expression matching, all patterns will be matched as exact strings.

Enables case-sensitive comparison.

Enables case-insensitive comparison.

Switches to the POSIX Basic regular expression matching.

Switches to the POSIX Extended regular expression matching.

The special statement regex allows you to alter the default regular expression type. For example, the following statement

regex :perl :scase

sets the default regular expression types to Perl-style, case-sensitive. The settings of regex statement regard only those patterns that appear after it in the configuration file and have force until the next occurrence of the regex statement.

A couple of examples:

if header[Subject] :perlre "(?<=(?<!foo)bar)baz"

This will match any Subject header whose value matches an occurrence of `baz' that is preceded by `bar' which in turn is not preceded by `foo'.
if header[Subject] :scase "^Re"

will match a Subject header whose value starts with `Re', but will not match it if it starts with `RE' or `re'.

When using POSIX regular expressions, the extended syntax is enabled by default. If you wish to use a basic regular expression, precede it with the :basic flag.

For the detailed description of POSIX regular expressions, See section `Regular Expression Library' in Regular Expression Library. For information about Perl-style regular expressions, refer to the Perl documentation.

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6.6 Action List

An action list is a list of action commands, which control processing of an outgoing messages. All action command names are case insensitive, so you can use for instance: `add' or `ADD' or `AdD', and so on.

6.6.1 Stop Action  Stopping the Processing
6.6.2 Call Action  Invoking Another Section
6.6.3 Adding Headers or Text  How to add a new header or body line(s).
6.6.4 Removing Headers  How to remove a message header line(s).
6.6.5 Modifying Messages  How to modify a message contents on-the-fly.
6.6.6 Inserting Files  How to append text files to an outgoing message.
6.6.7 Mail Encryption  How to encrypt a message on-the-fly.
6.6.8 Using an External Processor  How to process a message body using an external tool.
6.6.9 Quick Example  A quick example of using an action list.

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6.6.1 Stop Action

The stop command stops immediately the processing of the section. It may be used in the main RULE section as well as in any user-defined section. For example:

if not header[Content-Type] "text/plain; .*"

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6.6.2 Call Action

The call command allows to invoke a user-defined section much in the same manner as a subroutine in a programming language. The invoked section continues to execute until its end or the stop statement is encountered, whichever the first.

BEGIN myproc
if header[Subject] "Re: .*"
trigger "pgp"
  gpg-encrypt "my_gpg_key"

call myproc

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6.6.3 Adding Headers or Text

The add command allows you to add arbitrary headers or text to the message. To add a header, use the following syntax:

Command: add header `['name`]' string
Command: add `['name`]' string
For example:

add header[X-Comment-1] "GNU's Not Unix!"
add [X-Comment-2] "Support FSF!"

Command: add body text
Adds the text to the message body. Use of this command with `here document' syntax allows to append multi-line text to the message, e.g.:

add body <<-EOT

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6.6.4 Removing Headers

The command remove removes the specified header from the message. The syntax is:

Command: remove [flags] header `['string`]'
Command: remove [flags] `['string`]'

The name of the header to delete is given by string parameter. By default only those headers are removed whose names match it exactly. Optional flags allow to change this behavior. See section 6.5 Regular Expressions, for the detailed description of these.

An example:

remove ["X-Mailer"]
remove :regex ["^X-.*"]

The first example will remove the `X-Mailer:' header from an outgoing message, and the second one will remove all "X-*" headers.

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6.6.5 Modifying Messages

The action command modify allows to alter the headers or the body of the message.

Command: modify [flags] header `['key`]' `['new-key`]'
Command: modify [flags] `['key`]' `['new-key`]'

For each header whose name matches key, replaces its name with new-key. If key is a regular expressions, new-key may contain back references. For example, the following statement will select all headers whose names start with `X-' and change their names to begin with `X-Old-':

modify header :re ["X-\(.*\)"] ["X-Old-\1"]

Command: modify [flags] header `['key`]' value
Command: modify [flags] `['key`]' value

For each header whose name matches key, changes its value to value. For example:

modify [Subject] "New subject"

This statement sets the new value to the Subject header.

Every occurrence of unescaped `&' in the new value will be replaced by the old header value. To enter the `&' character itself, escape it with two backslash characters (`\\'). For example, the following statement

modify [Subject] "[Anubis \\& others] &"

prepends the Subject header with the string `[Anubis & others]'. Thus, the header line

Subject: Test subject

after having been processed by Anubis, will contain:

Subject: [Anubis & others] Test subject

Command: modify [flags] header `['key`]' `['new-key`]' value
Command: modify [flags] `['key`]' `['new-key`]' value

Combines the previous two cases, i.e. changes both the header name and its value, as shown in the following example:

modify header [X-Mailer] [X-X-Mailer] "GNU Anubis"

Command: modify [flags] body `['key`]'
Removes all occurrences of key from the message body. For example, this statement will remove every occurrence of the word `old':

modify body ["old"]

Command: modify [flags] body `['key`]' string
Replaces all occurrences of key with string. For example:

modify body :extended ["the old \([[:alnum:]]+\)"] "the new \1"

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6.6.6 Inserting Files

Command: signature-file-append yes-or-no
This action command adds at the end of a message body the `-- ' line, and includes a client's `~/.signature' file. Value `no' is the default.

Command: body-append file-name
This action command includes at the end of a message body the contents of the given file. If `file-name' does not start with a `/' character, it is taken relative to the current user home directory

Command: body-clear
Removes the body of the message

Command: body-clear-append file-name
Replaces the message body with the contents of the specified file. The action is equivalent to the following command sequence:

body-append file-name

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6.6.7 Mail Encryption

Command: gpg-passphrase passphrase
Specifies your private key's pass phrase for signing an outgoing message using the GNU Privacy Guard (a tool compatible with the Pretty Good Privacy). Of course, to protect your passwords in the configuration file use the 0600 (u=rw,g=,o=) permissions, otherwise GNU Anubis won't accept them. We recommend setting the `gpg-passphrase' once in your configuration file, e.g. at the start of RULE section.

GNU Anubis supports the GNU Privacy Guard via the GnuPG Made Easy library, available at http://www.gnupg.org/gpgme.html.

Command: gpg-encrypt gpg-keys
This command enables encrypting your outgoing message with the GNU Privacy Guard (Pretty Good Privacy) public key(s). gpg-keys is a comma separated list of keys (with no space between commas and keys).

gpg-encrypt "John's public key"

Command: gpg-sign gpg-signer-key
Command: gpg-sign `yes-or-default'
This command signs the outgoing message with your GNU Privacy Guard private key. Specify a passphrase with gpg-passphrase. Value `default' means your default private key, but you can change it if you have more than one private key.

For example:

gpg-sign default


gpg-passphrase "my office key passphrase"
gpg-sign office@example.key

Command: gpg-sign-encrypt gpg-keys[:gpg-signer-key]
Command: gpg-se gpg-keys[:gpg-signer-key]
This command simultaneously signs and encrypts your outgoing message. It has the same effect as gpg command line switch `-se'. The argument before the colon is a comma-separated list of PGP keys to encrypt the message with. This argument is mandatory. The second argument is optional and is separated from the first one by a colon (`:'). This argument specifies the signer key. In the absence of the second argument your default private key is used.

For example:

gpg-sign-encrypt John@example.key


gpg-se John@example.key:office@example.key

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6.6.8 Using an External Processor

Command: external-body-processor program [args]
Pipes the message body through program. program should be a filter program, that reads the text from the standard input and prints the transformed text on the standard output. The output from the program replaces the body of the message. args are any additional arguments the program may require.

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6.6.9 Quick Example

Here is a quick example of using an action list:

if header [X-Mailer] :re ".*"
   remove [X-Mailer]
   add [X-Comment] "GNU's Not Unix!"
   gpg-sign "my password"
   signature-file-append yes

The example above will remove (on-the-fly) the `X-Mailer:' line from an outgoing message, add an extra header line (`X-Comment:'), sign your message with your private key, and add a simple signature file from your home directory.

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6.7 Using Guile Actions

The name Guile stands for GNU's Ubiquitous Intelligent Language for Extensions. It provides a Scheme interpreter conforming to the R4RS language specification. GNU Anubis uses Guile as its extension language.

This section describes how to write GNU Anubis actions in Scheme. It assumes that the reader is sufficiently familiar with the Scheme language. For information about the language, refer to section `Top' in Revised(4) Report on the Algorithmic Language Scheme. For more information about Guile, See section `Overview' in The Guile Reference Manual.

6.7.1 Defining Guile Actions  
6.7.2 Invoking Guile Actions  

Predefined Guile Actions
6.7.3 Support for ROT-13  
6.7.4 Remailers Type-I  
6.7.5 Entire Message Filters  

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6.7.1 Defining Guile Actions

A Guile action is defined as follows:

(define (function-name header body . rest)

Its arguments are:

List of message headers. Each list element is a cons

(name . value)

where name is the name of the header field, and value is its value with final CRLF stripped off. Both name and value are strings.

A string containing the message body.

Any additional arguments passed to the function from the configuration file (see section 6.7.2 Invoking Guile Actions). This argument may be absent if the function is not expected to take optional arguments.

The function must return a cons whose car contains the new message headers, and cdr contains the new message body. If the car is #t, it means that no headers are changed. If the cdr is #t, it means that the body has not changed. If the cdr is #f, Anubis will delete the entire message body.

As the first example, let's consider a no-operation action, i.e. an action that does not alter the message in any way. It can be written in two ways:

(define (noop-1 header body)
  (cons header body))
(define (noop-2 header body)
  (cons #t #t))

The following example is a function that deletes the message body and adds an additional header:

(define (proc header body)
  (cons (append header
                (cons "X-Body-Deleted" "yes"))

Let's consider a more constructive example. The following function checks if the Subject header starts with string `ODP:' (a Polish equivalent to `Re:'), and if it does, the function replaces it with `Re:'. It always adds to the message the header

X-Processed-By: GNU Anubis

Additionally, if the optional argument is given, it is appended to the body of the message.

(define (fix-subject hdr body . rest)
  "If the Subject: field starts with characters \"ODP:\", replace
them with \"Re:\".
If REST is not empty, append its car to BODY"
  (cons (append
	 (map (lambda (x)
		(if (and (string-ci=? (car x) "subject")
			 (string-ci=? (substring (cdr x) 0 4) "ODP:"))
		    (cons (car x)
			  (string-append "Re:"
					 (substring (cdr x) 4)))
	 (list (cons "X-Processed-By" "GNU Anubis")))
	(if (null? rest)
	    (string-append body "\n" (car rest)))))

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6.7.2 Invoking Guile Actions

The Guile actions are invoked from the RULE section using the guile-process command. Its syntax is:

Scheme Function: function args

The name of the Guile function to be invoked.

Additional arguments. These are passed to the function as its third argument (rest).

To pass keyword arguments to the function, use the usual Scheme notation: `#:key'.

As an example, let's consider the invocation of the fix-subject function, defined in the previous subsection:

guile-process fix-subject <<-EOT
                                Kind regards,
                                Antonius Block

In this example, the additional argument (a string of three lines) is passed to the function, which will add it to the message of the body.

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6.7.3 Support for ROT-13

The ROT-13 transformation is a simple form of encryption where the letters A-M are transposed with the letters L-Z. It is often used in Usenet postings/mailing lists to prevent people from accidentally reading a disturbing message.

GNU Anubis supports ROT-13 via a loadable Guile function. To enable this support, you will have to add the following to your GUILE section:

guile-load-program rot-13.scm

Then, in your RULE section use:

Scheme Function: rot-13 keyword-arguments
The command accepts the following keyword-arguments:

Encrypt the entire body of the message

Encrypt the `Subject' header.

For example:

trigger "rot-13.*body"
 guile-process rot-13 #:body

trigger "rot-13.*subj"
 guile-process rot-13 #:subject

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6.7.4 Remailers Type-I

GNU Anubis supports remailers of type I. The support is written entirely in Scheme. To enable it you need to specify the following in the GUILE section of your configuration file:

guile-load-program remailer.scm

To send the message via a remailer, use the following command in the RULE section:

Scheme Function: remailer-I keyword-arguments
The keyword-arguments specify the various parameters for the remailer. These are:

#:rrt string
This is the only required keyword argument. It sets the value for the Request Remailing To line. string should be your actual recipient's email address.

#:post news-group
Adds the `Anon-Post-To: news-group' line, and prepares the message for sending it to the Usenet via a remailer. Note, that this is only possible with remailers that support `Anon-Post-To:' header.

#:latent time
Adds the `Latent-Time:' line, that causes a remailer to keep your message for specified time before forwarding it.

Adds random suffix to the latent time.

#:header string
Adds an extra header line to the remailed message.


trigger "remail:(.*)/(.*)"
 guile-process remailer-I \
             #:rrt antonius_block@helsingor.net \
             #:post \1 \
             #:latent \2 \
             #:header "X-Processed-By: GNU Anubis & Remailer-I"

Some remailers require the message to be GPG encrypted or signed. You can achieve this by placing gpg-encrypt or gpg-sign statement right after the invocation of remailer-I, for example:

trigger "remail:(.*)/(.*)"
 guile-process remailer-I \
             #:rrt antonius_block@helsingor.net \
             #:post \1 \
             #:latent \2 \
             #:header "X-Processed-By: GNU Anubis & Remailer-I"
 gpg-sign mykey

See section 6.6.7 Mail Encryption, for more information on mail encryption in GNU Anubis.

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6.7.5 Entire Message Filters

There may be some cases when you need to use an external filter that processes the entire message (including headers). You cannot use external-body-processor, since it feeds only the message body to the program. To overcome this difficulty, GNU Anubis is shipped with `entire-msg.scm' module. This module provides Scheme function entire-msg-filter, which is to be used in such cases.

Scheme Function: entire-msg-filter program [args]
Feeds entire message to the given program. The output from the program replaces message headers and body.

Full pathname of the program to be executed.

Any additional arguments it may require.

Suppose you have a program /usr/libexec/myfilter, that accepts entire message as its output and produces on standard output a modified version of this message. The program takes as its argument he name of a directory for temporary files. The following example illustrates how to invoke this program:

guile-load-program entire-msg.scm

guile-process entire-msg-filter /usr/libexec/myfilter /tmp

Another function defined in this module is openssl-filter:

Scheme Function: openssl-filter program [args]

This function is provided for use with openssl program. Openssl binary attempts to rewind its input and fails if the latter is a pipe, so openssl cannot be used with entire-msg-filter. Instead, you should use openssl-filter. Its arguments are:

Path to openssl binary.

Its arguments

See section 10. Using S/MIME Signatures, for an example of use of this function.

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7. Invoking GNU Anubis

The anubis executable acts like a daemon. The behavior of program is controlled by two configuration files, which have a higher priority than command line options. See section 5. Configuration, for details.

GNU anubis supports the following command line options:

`--altrc file'
Specify alternate system configuration file.

`--bind [host:]port'
Specify the TCP port on which GNU Anubis listens for connections. The default host value is `INADDR_ANY', and default port number is 24 (private mail system).

Run the configuration file syntax checker. Optional level specifies the verbosity level. The following levels are allowed:

Display only errors. This is the default.

Print the syntax tree after parsing the file.

As `1', but also prints the parser traces.

As `2', but also prints the lexical analyzer traces.

Debug mode.

Foreground mode.

Print short usage summary and exit.

`--local-mta file'
Execute a local SMTP server, which works on standard input and output (inetd-type program). This option excludes the `--remote-mta' option.

`--mode mode-name'
`-m mode-name'
Selects Anubis operation mode. Allowed values for mode-name are `transparent' (default) and `auth'. See section 4. Authentication, for the detailed discussion of Anubis operation modes.

Ignore system configuration file.

Do not check a user config file permissions.

`--remote-mta host[:port]'
Specify a remote SMTP host name or IP address, which GNU Anubis will connect and forward mail to (after a processing). The default port number is 25.

Work silently.

Print a list of configuration options used to build GNU Anubis.

Use the SMTP protocol (OMP/Tunnel) as described in RFC 821 on standard input and output.

Work noisily.

Print version number and copyright.


$ anubis --remote-mta smtp-host:25

Run GNU Anubis on port number 24 (private mail system). Note that you must have root privileges to use port number lower than 1024. Make the tunnel between your localhost:24 and smtp-host:25.

$ anubis -f --remote-mta smtp-host:25

Same as above, but run GNU Anubis in a foreground mode.

$ anubis -f --local-mta /usr/sbin/sendmail -- sendmail -bs

Similar to above, but create a tunnel between localhost:24 and a local program (local MTA). In this example local program is sendmail with `-bs' command line option. The `-bs' option forces sendmail to work on standard input and output.

$ anubis --norc --remote-mta smtp-host:25

Do not read the system configuration file, make the tunnel between localhost:24 and smtp-host:25.

$ anubis --bind localhost:1111 --remote-mta smtp-host:25

Create the tunnel between localhost:1111 and smtp-host:25.

$ anubis -i

Use the SMTP protocol (OMP/Tunnel) as described in RFC 821 on standard input and output.

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8. Sample Beginning

By default, GNU Anubis binds to port number 24 (private mail system), so there shouldn't be any conflict with your local MTA (Mail Transport Agent). You just have to reconfigure your MUA (Mail User Agent) to make it talk to GNU Anubis directly on port number 24. All MUAs are normally set up to talk directly to the MTA, so you must change their settings and specify GNU Anubis' port number as their target. This makes GNU Anubis to work as an outgoing mail processor between your MUA and the MTA. Read your MUA's documentation for more information.

Now you must choose whether you want to connect GNU Anubis with a remote or local SMTP host via TCP/IP or a local SMTP program, which works on standard input and output. In the first case, specify the following option:

REMOTE-MTA smtp-host:25

In the second case (local SMTP program), specify this:

LOCAL-MTA /path/to/your/mta/mta-executable -bs

Please note that the `-bs' command line option is a common way to run MTAs on standard input and output, but it is not a rule. Read your local MTA's documentation, how to get it working on standard input and output.

If you would like to run GNU Anubis on port number 25 (which is a default value for the SMTP) or any other port number, then you must specify the `bind' keyword. For instance, the following code will bind GNU Anubis to `localhost:25':

BIND localhost:25

This can make a conflict between GNU Anubis and your local MTA, which usually listens on port number 25. To solve this problem, you can for instance disable the MTA and specify the `local-mta' keyword, or run MTA on port number different than GNU Anubis' port number (e.g. 1111). Please read your local MTA's documentation about this topic. For example:

BIND localhost:25
REMOTE-MTA localhost:1111

Caution: Make sure that your local machine doesn't accept any incoming mail (i.e. it is not a POP or IMAP server), otherwise you cannot disable your MTA or change its port number!

All Mutt users, who would like to set up GNU Anubis between their MUA and MTA, should consider using the `msg2smtp.pl' Perl script from the `contrib' directory (part of the distribution).

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9. Using the TLS/SSL Encryption

According to the RFC 2246 document, the TLS (Transport Layer Security) protocol provides communications privacy over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The primary goal of the TLS Protocol is to provide privacy and data integrity between two communicating applications. The TLS protocol itself is based on the SSL 3.0 (Secure Socket Layer) protocol specification.

GNU Anubis supports the TLS/SSL (via the GnuTLS, a Transport Layer Security Library available at http://www.gnutls.org/, or OpenSSL, a cryptographic package available at http://www.openssl.org/), but your MTA must provide the STARTTLS command first. This can be checked by:

$ telnet your-smtp-host 25
  ehlo your-domain-name

The server will response with all its available commands. If you see the STARTTLS, then you can use the TLS/SSL encryption. If your MUA doesn't support the TLS/SSL encryption, but your MTA does, then you should use the `oneway-ssl' keyword in your configuration file. Before using the TLS/SSL encryption, you must generate a proper private key and a certificate. You can do it simply with:

$ cd anubis-directory
$ ./build/keygen.sh

This will create the `anubis.pem' file. For example copy this file to `/usr/share/ssl/certs/'. Next, edit your configuration file by adding:

ssl yes
ssl-key path-to-the-private-key
ssl-cert path-to-the-certificate

For example:

ssl-key /usr/share/ssl/certs/anubis.pem
ssl-cert /usr/share/ssl/certs/anubis.pem

Caution: Each client can specify its own private key and a certificate by adding the `ssl-key' and `ssl-cert' keywords in its own user configuration file.

See section 5.2.5 Encryption Settings, for details.

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10. Using S/MIME Signatures

Anubis version 4.0 does not yet provide built-in support for S/MIME encryption or signing. To encrypt or sign messages using S/MIME, you will have to use external programs. Usually such programs require the whole message as their input, so simply using external-body-processor will not work. GNU Anubis distribution includes a special Guile program, `entire-msg.scm', designed for use with such programs. For its detailed description, please refer to 6.7.5 Entire Message Filters. This chapter addresses a special case of using it with openssl to sign outgoing messages.

To use openssl for S/MIME signing, invoke it using openssl-filter function defined in `entire-msg.scm'. You will have to supply at least -sign and -signer arguments to the program. Notice, that you should not specify any input or output files.

The following example illustrates this approach:

guile-load-program entire-msg.scm

guile-process openssl-filter /usr/local/ssl/bin/openssl \
              smime -sign -signer FILE

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11. Using Mutt with Anubis

At the time of this writing mutt(5)is not able to send mail via SMTP channell, instead it invokes local mailer program to transmit the message. There are at least three possible ways to overcome this difficulty:

  1. Using mail.remote from GNU mailutils
  2. Using msg2smtp.pl script provided with Anubis
  3. Using a patch by Steven Engelhardt (patch-version.sde.libesmtp.3) that enables mutt to use SMTP.

The following sections discuss each method in detail.

11.1 Using GNU mailutils as an interface to mutt  Using GNU Mailutils
11.2 Using msg2smtp.pl as an interface to mutt  Using msg2smtp.pl
11.3 Patching mutt  Enabling mutt to talk
11.4 Comparison of the Three Interface Methods  Which method to choose?

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11.1 Using GNU mailutils as an interface to mutt

GNU Mailutils is a collection of utilities for handling electronic mail. It includes lots of programs necessary for dealing with e-mail messages. One of them is mail.remote, which is designed as a drop-in replacement for sendmail to forward all mail directly to an SMTP gateway. Its interface is compatible with sendmail which makes the program especially useful as an interface between mutt and anubis. The package can be downloaded from ftp://ftp.gnu.org/gnu/mailutils or any of the mirrors (See http://www.gnu.org/order/ftp.html for a complete list of these. Please, select the mirror closest too you). The complete information about the package is available from its home page at http://www.gnu.org/software/mailutils/

To use mail.remote, first download and install GNU mailutils (as usual the package is shipped with files `README' and `INSTALL' which provide the necessary guidelines). Then add to your `.muttrc' file the following line:

set sendmail="mail.remote smtp://hostname[:port]"

where mail.remote stands for the full file name of mail.remote utility, hostname and optional port specify the host name (or IP address) of the machine running anubis and the port it listens on. Notice, that default port value for mail.remote is 25, which means that in most cases you will have to specify it explicitely.

For example, suppose you run anubis on machine `anubis.domain.org' and that it listens on port 24. Let's also assume you have installed mailutils in the default location, so that full file name of mail.remote is `/usr/local/libexec/mail.remote'. Then, your `.muttrc' will contain:

set sendmail="/usr/local/libexec/mail.remote \

(the line being split for readability).

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11.2 Using msg2smtp.pl as an interface to mutt

GNU Anubis is shipped with msg2smtp.pl -- a perl script designed as an interface between it and mutt. The script is kindly contributed by Michael de Beer.

The script is located in the subdirectory `contrib' of GNU Anubis distribution. To use it:

  1. Make sure its first line correctly refers to the full file name of the perl interpreter on your system. By default the first line reads


    If the file name after `!' differs from the actual file name of the perl interpreter, update it. For example, if perl is installed in `/usr/local/bin/perl', the first line of msg2smtp.pl should read


  2. Copy the script to any convenient location. Simply running cp will do, e.g.

    cp anubis-4.0/contrib/msg2smtp.pl /usr/local/libexec

  3. Add to your `.muttrc' the following line:

    set sendmail="/usr/local/libexec/msg2smtp.pl -h hostname -p port"

    where hostname and port specify the host name (or IP address) of the machine running anubis and the port it listens on, respectively.

Complete description of msg2smtp.pl and a discussion of its command line switches can be found in file `contrib/msg2smtp.txt'.

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11.3 Patching mutt

Steven Engelhardt modified mutt so that it is able to use SMTP to transfer messages. For the time being the patch is not accepted by the mainline mutt distribution, but one of the authors of GNU Anubis(6), has tested it extensively and has found it to be quite adequate for interfacing between anubis and mutt. The patch is described in detail at http://www.deez.info/sengelha/projects/mutt/libesmtp/ and is available for mutt versions 1.4.x and 1.5.3.

To use it, follow the instructions on the page mentioned above. Once you compile the patched mutt you will be able to use the following new keywords in its configuration file:

set smtp_host = hostname
Sets the hostname or IP address of the remote SMTP host.

set smtp_port = port
Sets the port number to use.

set smtp_auth_username = user-name
Sets the username to use with SMTP AUTH command (optional).

So, assuming you run anubis on machine `anubis.domain.org' and it is listening on port 24, you will add to your `.muttrc' the following two lines:

set smtp_host = anubis.domain.org
set smtp_port = 24

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11.4 Comparison of the Three Interface Methods

The following short discussion summarizes the advantages and deficiencies of the three interface methods described in the previous sections. It could serve you as a guideline on which interface method to choose.

Using mail.remote


  1. Does not require modifying mutt.
  2. Is compatible with any version of mutt.
  3. Runs faster than msg2smtp.pl


  1. Running an external program to transmit the message is not the best idea. However, it is mutt default, anyway...
  2. Runs slower than directly connecting to anubis using SMTP

Using msg2smtp.pl


  1. Does not require modifying mutt.
  2. Is compatible with any version of mutt.


  1. See extprog.
  2. Runs slower than the other two methods (sending each message requires loading perl interpreter, which is rather expensive).

Using patch.sde.libesmtp.3


  1. Is the fastest of the three methods.
  2. Does not require any intermediate programs.


  1. Requires patching mutt, which is not always possible or acceptable.
  2. May not work for versions of mutt newer than 1.5.3 (but then, again, not necessarily so).

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12. Reporting Bugs

Please send any bug reports, improvements, comments, suggestions, or questions to bug-anubis@gnu.org.

Before reporting a bug, make sure you have actually found a real bug. Carefully reread the documentation and see if it really says you can do what you are trying to do. If it is not clear whether you should be able to do something or not, report that too; it's a bug in the documentation!

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13. Pixie & Dixie

-- THE END ---

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A. GNU Free Documentation License

Version 1.2, November 2002

Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
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Everyone is permitted to copy and distribute verbatim copies
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    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.


    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warrany Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.


    You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.


    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

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A.0.1 ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

  Copyright (C)  year  your name.
  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.2
  or any later version published by the Free Software Foundation;
  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
  A copy of the license is included in the section entitled ``GNU
  Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with...Texts." line with this:

    with the Invariant Sections being list their titles, with
    the Front-Cover Texts being list, and with the Back-Cover Texts
    being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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Concept Index

Jump to:   A   B   C   D   E   F   G   I   L   M   O   P   R   S   T   U  

Index Entry Section

Action List6.6 Action List
actions defined6.1 Actions
add6.6.3 Adding Headers or Text
add6.6.3 Adding Headers or Text
add6.6.3 Adding Headers or Text
allow-local-mta5.2.6 Security Settings
AUTH section5.1 AUTH Section
authentication4. Authentication

basic, flag6.5 Regular Expressions
bind5.2.1 Basic Settings
body-append6.6.6 Inserting Files
body-clear6.6.6 Inserting Files
body-clear-append6.6.6 Inserting Files
bugs12. Reporting Bugs

call6.6.2 Call Action
client2. Overview
command line7. Invoking GNU Anubis
Conditional statements6.2 Conditional Statements
configuration5. Configuration
CONTROL section5.2 CONTROL Section
control-priority5.2.6 Security Settings

daemon2. Overview
drop-unknown-user5.2.6 Security Settings

else, conditional statements6.2 Conditional Statements
encryption9. Using the TLS/SSL Encryption
entire message, filtering6.7.5 Entire Message Filters
entire-msg-filter6.7.5 Entire Message Filters
entire-msg.scm6.7.5 Entire Message Filters
ESMTP authentication5.2.4 ESMTP Authentication Settings
esmtp-allowed-mech5.2.4 ESMTP Authentication Settings
esmtp-anonymous-token5.2.4 ESMTP Authentication Settings
esmtp-auth5.2.4 ESMTP Authentication Settings
esmtp-auth-id5.2.4 ESMTP Authentication Settings
esmtp-authz-id5.2.4 ESMTP Authentication Settings
esmtp-generic-service5.2.4 ESMTP Authentication Settings
esmtp-hostname5.2.4 ESMTP Authentication Settings
esmtp-passcode5.2.4 ESMTP Authentication Settings
esmtp-password5.2.4 ESMTP Authentication Settings
esmtp-realm5.2.4 ESMTP Authentication Settings
esmtp-require-encryption5.2.4 ESMTP Authentication Settings
esmtp-service5.2.4 ESMTP Authentication Settings
ex, flag6.5 Regular Expressions
exact, flag6.5 Regular Expressions
extended, flag6.5 Regular Expressions
extension language5.4 GUILE Section
external-body-processor6.6.8 Using an External Processor

FDL, GNU Free Documentation LicenseA. GNU Free Documentation License
fi, conditional statements6.2 Conditional Statements
function6.7.2 Invoking Guile Actions

GNU mailutils11.1 Using GNU mailutils as an interface to mutt
GNU mailutils11.4 Comparison of the Three Interface Methods
GNU Privacy Guard, GnuPG6.6.7 Mail Encryption
GnuTLS9. Using the TLS/SSL Encryption
gpg-encrypt6.6.7 Mail Encryption
gpg-passphrase6.6.7 Mail Encryption
gpg-se6.6.7 Mail Encryption
gpg-sign6.6.7 Mail Encryption
gpg-sign6.6.7 Mail Encryption
gpg-sign-encrypt6.6.7 Mail Encryption
GPG/PGP private key6.6.7 Mail Encryption
GPG/PGP public key6.6.7 Mail Encryption
Guile5.4 GUILE Section
Guile6.7 Using Guile Actions
Guile Actions, defining6.7.1 Defining Guile Actions
GUILE section5.4 GUILE Section
guile-debug5.4 GUILE Section
guile-load-path-append5.4 GUILE Section
guile-load-program5.4 GUILE Section
guile-output5.4 GUILE Section
guile-process6.7.2 Invoking Guile Actions

icase, flag6.5 Regular Expressions
if, conditional statements6.2 Conditional Statements

local-mta5.2.1 Basic Settings
logfile5.2.2 Output Settings
loglevel5.2.2 Output Settings

mail.remote11.1 Using GNU mailutils as an interface to mutt
mail.remote11.4 Comparison of the Three Interface Methods
mailutils11.1 Using GNU mailutils as an interface to mutt
mailutils11.4 Comparison of the Three Interface Methods
message submission daemon2. Overview
mode5.2.1 Basic Settings
modify6.6.5 Modifying Messages
modify6.6.5 Modifying Messages
modify6.6.5 Modifying Messages
modify6.6.5 Modifying Messages
modify6.6.5 Modifying Messages
modify6.6.5 Modifying Messages
modify6.6.5 Modifying Messages
modify6.6.5 Modifying Messages
msg2smtp.pl11.2 Using msg2smtp.pl as an interface to mutt
msg2smtp.pl11.4 Comparison of the Three Interface Methods
MTA, Mail Transport Agent2. Overview
MUA, Mail User Agent2. Overview
mutt11. Using Mutt with Anubis
mutt, using SMTP gateways11.3 Patching mutt
mutt, using SMTP gateways11.4 Comparison of the Three Interface Methods

OpenSSL9. Using the TLS/SSL Encryption
openssl10. Using S/MIME Signatures
openssl-filter6.7.5 Entire Message Filters
outgoing mail processor2. Overview
overview2. Overview

perl, flag6.5 Regular Expressions
perlre, flag6.5 Regular Expressions
Pretty Good Privacy, PGP6.6.7 Mail Encryption
problems12. Reporting Bugs
proxy2. Overview

re, flag6.5 Regular Expressions
regex, flag6.5 Regular Expressions
remailer6.7.4 Remailers Type-I
remailer-I6.7.4 Remailers Type-I
remote-mta5.2.1 Basic Settings
remove6.6.4 Removing Headers
remove6.6.4 Removing Headers
rot-136.7.3 Support for ROT-13
rule system6. The Rule System
rule-priority5.2.6 Security Settings

sasl-allowed-mech5.1 AUTH Section
sasl-password-db5.1 AUTH Section
scase, flag6.5 Regular Expressions
Scheme5.4 GUILE Section
Secure Socket Layer, SSL9. Using the TLS/SSL Encryption
server2. Overview
settings5. Configuration
signature-file-append6.6.6 Inserting Files
Simple Mail Transport Protocol, SMTP2. Overview
smime10. Using S/MIME Signatures
smtp-greeting-message5.1 AUTH Section
smtp-help-message5.1 AUTH Section
SOCKS proxy5.2.3 Proxy Settings
socks-auth5.2.3 Proxy Settings
socks-proxy5.2.3 Proxy Settings
socks-v45.2.3 Proxy Settings
ssl5.2.5 Encryption Settings
ssl-cafile5.2.5 Encryption Settings
ssl-cert5.2.5 Encryption Settings
ssl-key5.2.5 Encryption Settings
ssl-oneway5.2.5 Encryption Settings
stop6.6.1 Stop Action
system configuration file5. Configuration

termlevel5.2.2 Output Settings
tracefile5.2.2 Output Settings
tracefile5.2.2 Output Settings
Transport Layer Security, TLS9. Using the TLS/SSL Encryption
Triggers6.3 Triggers
tunnel2. Overview

user configuration file5. Configuration
user-notprivileged5.2.6 Security Settings

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It is not a serious restriction, however. The user may install Anubis on his machine for the sole purpose of SMTP authentication, as Pixie-Dixie suggests.


See http://www.mysql.com.


See http://www.postgres.org.


Make sure to run anubisusr in background, so it does not slow down your normal login sequence


versions 1.4.1 and 1.5.3


Sergey Poznyakoff, blame it on him:^)


The scheme implemented currently is a bit different. First, the config-sender program issues an EXAMINE command that fetches the contents of the user configuration file from the server. Then, it compares it with the local copy kept on the client machine. If the copies differ, config-sender issues UPLOAD and thus updates the configuration on the server.

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Table of Contents

[Top] [Contents] [Index] [ ? ]

Short Table of Contents

1. GNU Anubis
2. Overview
3. Glossary of Frequently Used Terms
4. Authentication
5. Configuration
6. The Rule System
7. Invoking GNU Anubis
8. Sample Beginning
9. Using the TLS/SSL Encryption
10. Using S/MIME Signatures
11. Using Mutt with Anubis
12. Reporting Bugs
13. Pixie & Dixie
A. GNU Free Documentation License
Concept Index

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