For some reason Gmail has started blocking mailman administrative emails to someone who's an admin on a list I host. Their SMTP 552 error message points to <https://support.google.com/mail/?p=BlockedMessage>, which implies the "problem" is the URLs in the email, but is otherwise completely unhelpful.
If anyone here has any pull with Gmail postmasters, could you please suggest to them that they whitelist messages that are as consistent and well-known as mailman's admin and moderator messages?
