I have just set up mailcow: dockerized on a VPS and I am using Sieve postfilters to forward emails from certain mailboxes to associated @gmail.com addresses. The filters are excluding mails with the “X-Spam-Flag: YES” header from Rspamd to minimise the amount of spam that might be sent on from my mail server into Gmail. I am using SPF with DKIM and ARC signing, and have DMARC reports configured.
This setup seems to be working fine for most emails.
However one mailbox receives a regular email from Twitter that they have subscribed to, and Gmail responds to Postfix with this message when trying to forward/relay these specific emails.:
Our system has detected an unusual rate of 421-4.7.28 unsolicited mail originating from your IP address. To protect our 421-4.7.28 users from spam, mail sent from your IP address has been temporarily 421-4.7.28 rate limited.
So far these emails eventually get delivered to the Gmail address, and the message itself is not flagged as Spam in Gmail when it does get delivered. So far I have forwarded approx. 35 emails to this Gmail address over the last two days, of which Gmail has flagged 4 or 5 as Spam. I don’t think this would count as an “unusual rate of unsolicited mail”, but I am concerned that this is affecting my sending reputation with Gmail.
Is there anything I can do to improve this situation?