I'll tell you what I'm doing over on the SSI Maillist. I've set Yahoo to where new members have to be approved. When I get the E-mail, I look to see if they've filled out the comment section with anything which seems at all on-topic for SSI (ignoring more general things like, "Thank you for letting me join your wonderful group". If they haven't, I send them an E-mail asking them what subjects, among those researched by SSI, interests them. Most spammers can't be bothered to learn enough about the maillist to give an on-topic answer. If I get none, then I let their application expire.

Thanks, Mike. It's more work for you, and I appreciate that you are
doing it. Spam sucks.