ispell-message

ispell-message is an interactive autoloaded compiled Lisp function in `ispell.el'.

It is bound to <menu-bar> <tools> <spell> <ispell-message>.

(ispell-message)

Check the spelling of a mail message or news post.
Don't check spelling of message headers except the Subject field.
Don't check included messages.

To abort spell checking of a message region and send the message anyway,
use the `x' command. (Any subsequent regions will be checked.)
The `X' command aborts sending the message so that you can edit the buffer.

To spell-check whenever a message is sent, include the appropriate lines
in your init file:
(add-hook 'message-send-hook 'ispell-message) ;; GNUS 5
(add-hook 'news-inews-hook 'ispell-message) ;; GNUS 4
(add-hook 'mail-send-hook 'ispell-message)
(add-hook 'mh-before-send-letter-hook 'ispell-message)

You can bind this to the key C-c i in GNUS or mail by adding to
`news-reply-mode-hook' or `mail-mode-hook' the following lambda expression:
(function (lambda () (local-set-key "\C-ci" 'ispell-message)))