See The Emacs Manual. • Normally, Emacs expands aliases when you send the message. To expand them before this, use M-x expand-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-: (build-mail-aliases) to make Emacs reread ~/.mailrc. • 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-mode-hook ‘mail-abbrevs-setup) Note that the aliases are expanded automatically only after you type a word-separator character (e.g. or ,). You can force their expansion by moving point to the end of the alias and typing C-x a e (M-x expand-abbrev).