[MlMt] MailMate "remembers" to send HTML to certain recipients... help it forget!

[Sam Hathaway]

Hi,

I think this has been covered before, but I can’t seem to find it in 
the archives. I have configured MailMate to never send HTML. That is, I 
have the following settings in the Composer preferences:

Preview: Display [when generating HTML]
Replying/Forwarding HTML: [Never embed]
Embedding method: [Scoped Stylesheet]
[√] Warn before discarding HTML when editing
Rich Text (HTML): Markup syntax: [none]
Default theme is [Standard]
Styling method: [Inlining (recommended]
[ ] Generate HTML even if only for styling
Highlight code using [Nothing]
Math language: [None]

Still, when I reply to certain people, or even address new messages to 
these people, the preview pane pops up and the message is sent with an 
HTML part. It seems that if I (erroneously) sent someone an HTML message 
in the past, MailMate remembers this and insists on sending HTML in the 
future.

How can I make MailMate forget?
-sam