On: Why does Gmail hate my domain?

[kazinator]

Google mail's spam filter delivers spams to users; it just classifies it into a different folder.

In this case, the mail was bounced at the SMTP level, and the bounce is (strangely) identified as coming from Google Groups.

"Mark as safe" will not SMTP non-delivery problems, I think, just the mis-classification of e-mail as spam at the folder delivery level.