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6.4.13.3 Mail Spool

The nnml spool mail format isn't compatible with any other known format. It should be used with some caution.

If you use this back end, Gnus will split all incoming mail into files, one file for each mail, and put the articles into the corresponding directories under the directory specified by the nnml-directory variable. The default value is ~/Mail/.

You do not have to create any directories beforehand; Gnus will take care of all that.

If you have a strict limit as to how many files you are allowed to store in your account, you should not use this back end. As each mail gets its own file, you might very well occupy thousands of inodes within a few weeks. If this is no problem for you, and it isn't a problem for you having your friendly systems administrator walking around, madly, shouting “Who is eating all my inodes?! Who? Who!?!”, then you should know that this is probably the fastest format to use. You do not have to trudge through a big mbox file just to read your new mail.

nnml is probably the slowest back end when it comes to article splitting. It has to create lots of files, and it also generates NOV databases for the incoming mails. This makes it possibly the fastest back end when it comes to reading mail.

Virtual server settings:

nnml-directory
All nnml directories will be placed under this directory. The default is the value of message-directory (whose default value is ~/Mail).
nnml-active-file
The active file for the nnml server. The default is ~/Mail/active.
nnml-newsgroups-file
The nnml group descriptions file. See Newsgroups File Format. The default is ~/Mail/newsgroups.
nnml-get-new-mail
If non-nil, nnml will read incoming mail. The default is t.
nnml-nov-is-evil
If non-nil, this back end will ignore any NOV files. The default is nil.
nnml-nov-file-name
The name of the NOV files. The default is .overview.
nnml-prepare-save-mail-hook
Hook run narrowed to an article before saving.
nnml-use-compressed-files
If non-nil, nnml will allow using compressed message files. This requires auto-compression-mode to be enabled (see Compressed Files). If the value of nnml-use-compressed-files is a string, it is used as the file extension specifying the compression program. You can set it to ‘.bz2’ if your Emacs supports it. A value of t is equivalent to ‘.gz’.
nnml-compressed-files-size-threshold
Default size threshold for compressed message files. Message files with bodies larger than that many characters will be automatically compressed if nnml-use-compressed-files is non-nil.

If your nnml groups and NOV files get totally out of whack, you can do a complete update by typing M-x nnml-generate-nov-databases. This command will trawl through the entire nnml hierarchy, looking at each and every article, so it might take a while to complete. A better interface to this functionality can be found in the server buffer (see Server Commands).