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
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:
nnmldirectories will be placed under this directory. The default is the value of
message-directory(whose default value is ~/Mail).
nnmlserver. The default is ~/Mail/active.
nnmlgroup descriptions file. See Newsgroups File Format. The default is ~/Mail/newsgroups.
nnmlwill read incoming mail. The default is
nil, this back end will ignore any NOV files. The default is
nnmlwill allow using compressed message files. This requires
auto-compression-modeto be enabled (see Compressed Files). If the value of
nnml-use-compressed-filesis 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
tis equivalent to ‘.gz’.
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
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).