"Prefer Plain Text" heuristics

Future changes to how mailbox related state is saved could possibly allow you to at least make this setting depend on the currently selected mailbox, for example, to only use it for mailing list mailboxes.

But I think a solution similar to the Image Blocking setting (in the Security preferences pane) might make more sense. In any case, I'm open to providing some configurability.

I wonder if some regex-type filtering on messages would be possible?

I receive many hand-written list emails that are either entirely plain text, or very lightly formatted, that insist on the text being in the html message part with a generic "You need an email client supporting text/html to view the content of this email." always in the plain text message part, or just ".". This means MailMate always shows me the plain text message part, since it is present and that is my preference, and I must then switch to HTML to read the actual message. Of course these are all from badly configured mailers, but given how consistent these non-contentful plain text parts are, it is probably easy to filter. Other ones I would probably set a regex filter for are ones that dump html source into the plain text part.

Thanks.

@Sandy: I would be a bit worried about false positives on this regexp, but since the result would just be to show HTML for a message which did not really warrant it then it might be fine. The default would have to be to always show plain text. Many users enable it since they consider all HTML to be unsafe (and it would be easy to use this feature to trick MailMate to show arbitrary HTML).