Getting error " 15] Our system has detected that this message is 421-4.7.0 suspicious due to the very low reputation of the sending IP address" when forwarding to gmail.com

I’ve setup everything ok in MiaB - I think - and my admin status shows that everything is on green for my domain, except for DNSSEC which my domain name provider doesn’t support for my extension. Still, I am getting the error

15] Our system has detected that this message is 421-4.7.0 suspicious due to the very low reputation of the sending IP address

when forwarding emails to a gmail.com address. By looking at the logs, it does seem that Gmail is blocking genuine emails too.

I’ve tried to check Google’s docs related to the matter, but I can’t find anything special that I could do. Only thing that seems relevant is that MiaB (or Postfix in this case) would change the headers or the content of the email somehow, but I don’t think that’s happening either.

And when I send emails to http://www.mail-tester.com I get a full 10/10 score.

Can anyone help me with this issue please? The domain in question is paul.fi.

EDIT: After a bit of Googeling (https://www.digitalocean.com/community/questions/temporarily-rate-limited-from-google-in-mail-relay), I stumbled upon something called SRS (https://en.wikipedia.org/wiki/Sender_Rewriting_Scheme) that apparently should be used for cases like this. Does MiaB support SRS? And is this my problem?

Did you see this thread? Implement SPF:SRS

Do non-forwarded emails get sent OK?

Verifying your domain with Google Postmaster Tools might help: https://support.google.com/mail/answer/6227174?hl=en

I did verify my domain on Google Postmaster Tools, but it’s not yet showing any information. I do hope it would tell me more in-depth what might be wrong.

Direct mails always go through (in my tests). And it’s not like all forwards would get rejected by Google, it’s just that I recently saw a trend of increasingly more emails getting stuck in the queue and unable to be delivered to Google. I was wondering if there’s anything I can do “to improve the reputation of my IP”?

But did you read that thread?

No, if you have already set up your domain on postmater tools, that’s as good as it gets.

And, of course: if people are marking your emails as spam, then Google will consider your domain spammy.

You can also verify your ip adres of your box with http://www.mxtoolbox.com