Function: mail-abbrevs-mode

Toggle abbrev expansion of mail aliases (Mail Abbrevs mode).
With a prefix argument ARG, enable Mail Abbrevs mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.

Mail Abbrevs mode is a global minor mode. When enabled,
abbrev-like expansion is performed when editing certain mail
headers (those specified by `mail-abbrev-mode-regexp'), based on
the entries in your `mail-personal-alias-file'. (fn &optional ARG)

Variable: mail-abbrevs-mode

Non-nil if Mail-Abbrevs mode is enabled.
See the command `mail-abbrevs-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `mail-abbrevs-mode'.