2001021608MTrunk. This is related to error handling problem in 57083. In preference, Send Format is set to Ask me what to do. In Mail compose window, Format is Autodetect. In Mail/News Account Settings, Compose as HTML is checked ON. Compose a message that contains characters not supported as in bug 57083. Send and get the warning. Since it is not your fault that those characters can not be handled by Mozilla, you just OK to proceed and message is sent. The result: you never get a chance to be asked what to do about the format.
I did not see the problem using win32 6.01. It may be a Macintosh specific.
I have realized this has nothing to do with character code warnings. Mozilla does not care if the text is variable width. It simply decides to send in plain text if there is no other HTML element. Updating summary and component.
Reassign to ducarroz.
Looks like it is fixed in 022304 build for MacOS. Resolving as WFM
Checked 04/02 Mac trunk build. Marked it as verified.