137: Why doesn't Emacs expand my aliases when sending mail?

  * You must separate multiple addresses in the headers of the mail buffer
    with commas.  This is because Emacs supports RFC822 standard addresses
    like this one:

      To: Willy Smith <wks@xpnsv.lwyrs.com>

    However, you do not need to separate addresses with commas in your
    .mailrc file.

    WARNING: Emacs breaks up aliases in the .mailrc file into multiple
    addresses both on commas and on whitespace, regardless of any use of
    quotes.  This is probably a bug.  You can get around this by directly
    setting the value of mail-aliases.

  * Emacs normally only reads the ".mailrc" file once per session, when you
    start to compose your first mail message.  If you edit .mailrc, you can
    type "M-ESC (build-mail-aliases) RET" to make Emacs reread .mailrc.
    (You have to include the parentheses where they are shown!)

  * Emacs does not interpret vendor-specific additions to the format of the
    .mailrc file such as the "source" command.  It also ignores any "set"
    commands.  The only commands it looks at are "alias" and "group"
    commands.

  * If you like, you can expand mail aliases as abbrevs, as soon as you
    type them in.  To enable this feature, execute the following:

       (add-hook 'mail-setup-hook 'mail-abbrevs-setup)