Checklist of basic configuration
- rDNS / PTR - be sure that your mail server have got a hostname that points to your mail server IP and IP points to hostname
- DKIM / SPF and DMARC records are present and valid (you can check validity by sending single test letter to your GMail address you should have PASS for all three check points)
- RFC 8085 One-Click Unsubscribe
- In-body Unsubscribe
Optional: BIMI-record (if you’re sending on behalf of BIG company that have a trademark ONLY in specific region) you also need VMC so email-hosters would know that trademark belongs to your company and blah-blah-blah.