In a recent thread ("Fess up time - who did it?"), Winston replied with
the following (Thunderbird filter works the same):

quote
Advise adjust your filters.
Seamonkey example:
Tools Message Filters New WhackoPolitics
[From Contains] alt.california OR
[From Contains] politics OR
[From Contains] survivalism OR
[From Contains] cities
OK

OK?

--Winston
/quote

There's one final step - chose "action". I use "Ignore Thread" so
replies are filtered too.

Bob