Why do I get spam from Yahoo Groups?
If you're a member of any Yahoo Groups mailing lists, you may have noticed that some of the mail from the list is "spam". This happens a lot with some groups and rarely with others.
If our spam filter rejects these messages, Yahoo will remove you from the group, because messages to your mailbox are "undeliverable". This is a frustrating situation, because our spam filters are doing exactly what they're supposed to do.
Yahoo is the only large mailing list company we know of that works this way. Most companies avoid this problem with a simple technique: they send an extra "probe" message if they think your address might be invalid, removing you only if the "probe" bounces too.
Because we received so many complaints about (correctly) blocked spam leading to frequent removals from Yahoo Groups, we no longer block any spam that arrives via a Yahoo Groups membership, even if the message is definitely spam.
So if you join a Yahoo Groups list, you'll probably get some spam that we don't even try to block. If this bothers you (it certainly bothers us!), you might want to mention this problem to the group owner, suggesting he or she move the mailing list to a better service.