Howto Block Google Groups Spam in Rspamd
Spammers have learned that Google Groups is a convenient relay: create a free group, invite your victims, and push advertising, scams, or phishing through Google’s reputable infrastructure. Because the mails are delivered by Google, SPF, DKIM, and DMARC checks pass, and most filters stay quiet. If you do not have legitimate Google Group traffic into your mail system, you can block these messages with a tiny Rspamd rule.