David Bremner <david@tethera.net> writes:

> 1) Start emacs with emacs -Q
> 2) start sending a message with M-x message-mail
> 3) add "sign" tag with C-c C-m C-s
> 3) manually replace "sign with "sigencrypt", simulating failed attempt to 
>    manually change mode
> 4) add some text to the message, set a destination address and 
>    subject
> 5) send using C-c C-c
>
> The message is sent unencrypted, without any feedback to the user.  It
> seems that the correct response would be to refuse to send a message
> with malformed mml tags.

I've installed the following simple fix in the trunk.  Does it work for you?