How to block emails from some of yahoogroups but not all

[Budi Febrianto]

Dear All,

Just join this group, and the two emails from mailscanner.info (confirm and
welcome) tagged as spam :). Have manually added mailscanner.info as
whitelist. :).

Lot's of my users join the yahoogroups. It's not a problem, but... my
management want me to block emails from yahoogroups that contains that are
not allowed, like porn.

So I like to block emails from abc of yahoogroups.
I tried to simply blacklist emails from abc at yahoogroups.com, but it didn't
work.  Should I put it in SA as new rules? Any examples?

Best Regards