[verst]

Google Groups has a feature to automatically reject messages it considers to be Spam. That feature has always been quite terrible. The Google Groups Backend hasn't changed in a very long time.

https://support.google.com/groups/answer/2627595?hl=en

I personally always disable it for public groups and then rely on Spam filtering of the recipient inbox.

By the way - the bounce message you are seeing is what is sent when the Spam Classification Server determined your message to be Spam. The main reasons for that are things like sending from a bad IP, having certain keywords that are strongly correlated with Spam, or having domains in your message that are associated with Spam (based on other messages having been marked as Spam containing those domains).

[js2]

Re: Spam Classification Server. The problem went away when I moved my domain away from Google Apps. Literally, the exact same test message that I could not send when I had my domain on Google Apps, I could send once my domain was on Fastmail. Nothing changed, but that my message was now routing via Fastmail's SMTP servers vs the Google Apps SMTP servers. Same message content, same client IP, same MUA, same destination (I had a friend with a Google Apps domain setup a test group for me to send to on his domain).

[verst]

So you are saying:

Google Apps SMTP -> Google Apps Group (different domain) == FAIL

Fastmail SMTP -> Google Apps Group (different domain) == SUCCESS?

It's been a long time since I looked at this. We did have great internal tools to look up the classification of individual messages, including the top 10 deciding reasons for a given message classification. With a paid Google Apps domain a support rep investigating your ticket would eventually look at this tool to figure out what's going on.

[js2]

Yup, that's what was happening. Re: a paid account, I decided Fastmail was a better fit for my needs. Besides that, the problem was on the receiving end. So I somewhat disagree that I should have had to pay Google for someone to look into that.

[js2]

Yup, that's what was happening. Agree about a paid account, but I decided Fastmail was a better fit for my needs.