The real problem was due to the use of a <pre> tag to display plaintext messages. By default, it does not automatically cut long lines as with other tags. Some CSS stuff fixed the problem.
Fixed bad behaviour on some combinations between display mode and message available formats. (ie. plain/text or plain/html)
new: parameters module refactored. The API is more simple now, there is no need to provide a module name anymore, this last is automatically guessed. Also, a new 'label' field can be provide when declaring a new parameter. It will be used instead of the name.
new: email parsing refactored. My first attempt was really ugly. I did not really studied the various RFC describing how messages are formatted or what IMAP fetch queries can do. Now, I hope this new code will face better unknown types. At least, It will be simpler to update.
wip: #36, using tinyMCE (django-tinymce) to write messages in HTML. Currently, compose a new message is working pretty well. Answering or forwarding a message is still a mess...