Something occurred to me whilst I was setting up Apple Mail on my new Hackintosh.
It has an option to show plain text messages using a fixed width font. I have this set, but only because of the very occasional plain text message that uses tabs or spaces to line up items in multiple rows.
How about having a “smart” mode that attempts to spot this situation and use fixed width fonts only when necessary?
Off the top of my head I’d say that any mail containing a tab character or a run of two or more spaces (excluding the ends of lines), should trigger this mode.
Alternatively it could attempt to spot plain text formatting and actually convert it to formatted styled text. This would be trickier of course, but might allow it to do nice things like auto-converting common plain text idioms such as emphasis, underlining, bullet lists, and so on (I’m thinking of mark-up languages such as Markdown, or wiki-style formatting). I think Mail may actually do this already for emphasis, but it could be nice if it was expanded to cover other formatting.