Might it be possible to have a 'fixed width formatting' option when viewing messages on the web front end.
I second that motion.
If it is possible, might you be able to make a setting in each member's profile so they view all messages in this format, or if not, how about within each group's setting's details.
I'd rather have it be handy, as a view option when looking at messages. I'd have it apply to all the text/plain message bodies being displayed on the current page. I'd like to have it remembered as you navigate the site.
That is, I'd rather not have it tucked away in my profile where I have to go find it to change it, nor would I (as a member) want to have to pester the group admins to change it on a group-wide basis.