I meant to say To, my mistake there. That doesn’t negate my point, almost all mailing lists include a List-ID and/or other similar fields. That’s included even

I meant to say To, my mistake there. That doesn’t negate my point, almost all mailing lists include a List-ID and/or other similar fields. That’s included even when the list was bcc’d and is what you should be filtering on, not the To: field. Gmail even uses it automatically when you click on a message from a mailing list and click “filter messages like this”.