Hi, I have a ISPConfig server with a few domains. One client domain have a error to send emails to some providers. (from my ispconfig to anothers mail servers) host said: 550 5.7.1 Access to [email protected] not allowed (in reply to RCPT TO command) BUT, to some few providers, works. The Mx entry points to mail.example.com, and mail.example.com points A to my ISPConfig server. I have configured DMARC, DKIM and SPF and reverse IP. No blacklisted in any list. Can someone help me ?