Blacklist for To/CC in Thunderbird

"If you're mailing an email list, this is hard to avoid. The mailing list server can't see the bcc: header, so even with servers that do handle the case of not sending you your own messages twice, it won't work.

This has to be handled on the side of the client, but I'm not aware of an extension to do it. Probably something along the lines of ""delete duplicate emails""?"