In this chapter we have described the usual Emacs mode for editing and sending mail—Message mode. This is only one of several available modes. Prior to Emacs 23.2, the default mode was Mail mode, which is similar to Message mode in many respects but lacks features such as MIME support. Another available mode is MH-E (see MH-E in The Emacs Interface to MH).
You can choose any of these mail user agents as your preferred
method for editing and sending mail. The commands
C-x 4 m and
C-x 5 m use whichever agent you have
specified; so do various other parts of Emacs that send mail, such as
the bug reporter (see Bugs). To specify a mail user agent,
customize the variable mail-user-agent. Currently, legitimate
message-user-agent (Message mode)
sendmail-user-agent (Mail mode), gnus-user-agent, and
If you select a different mail-composition method, the information in this chapter about the mail buffer and Message mode does not apply; the other methods use a different format of text in a different buffer, and their commands are different as well.
Similarly, to specify your preferred method for reading mail,
customize the variable read-mail-command. The default is
rmail (see Rmail).