[Mailman-Developers] Preventing abuse of postorius

Apologies in advance if this isn't the right place to ask.

Almost every day I find outgoing emails from postorius stuck in my outbound mail queue. It seems like the anonymous_subscribe route is being used to send mail to unwitting targets. I'd rather not be operating a relay being used to DDoS people's mailboxes.

Any suggestions on out of the box solutions?

I know captcha's and such are imperfect, and a losing battle, but as an Internet old-timer (I was at the first IETF meeting), I feel obligated to at least try to contribute to a solution; I'm a Python programmer, but not a Djangoist.

Thanks, Phil