The message-mail-alias-type variable controls what type of mail
alias expansion to use. Currently only one form is supported—Message
uses mailabbrev to handle mail aliases. If this variable is
nil, no mail alias expansion will be performed.
mailabbrev works by parsing the /etc/mailrc and
~/.mailrc files. These files look like:
alias lmi "Lars Magne Ingebrigtsen <larsi@ifi.uio.no>"
alias ding "ding@ifi.uio.no (ding mailing list)"
After adding lines like this to your ~/.mailrc file, you should
be able to just write `lmi' in the To or Cc (and so
on) headers and press SPC to expand the alias.
No expansion will be performed upon sending of the message—all expansions have to be done explicitly.