> [and indeed, I do for several lists I'm on] but I haven't seen a mail
> agent that has a 'followup' button [or even fancier, and "unsubscribe me"
> button that automatically uses the List-unsubscribe: stuff...]
Pegasus Mail (Windows) has for quite some time supported the List-
Subscribe, List-Unsubscribe, and List-Help headers. Click on the
"subscription options" item (conveniently located at the top of the
message) and a dialog pops up with buttons for sub/unsub/help.
I use its regex filtering on List-Id to move list messages to folders.
'Reply' supports several options (unfortunately not configurable per list)
which you can set as default or have it remember your most recent choice.