If your domain's MX (Mail Exchange) records are pointing to the wrong server, that server will reject the mail because it doesn't recognize the domain as its own.
cat /opt/zimbra/log/mailbox.log | grep "SASL" zimbra relay access denied
For applications (scanners, CRMs), ensure they support authenticated SMTP on port 587. If not, consider a local SMTP relay. If your domain's MX (Mail Exchange) records are
The error in Zimbra typically occurs when the Mail Transfer Agent (MTA) is asked to forward an email to an external domain but does not recognize the sender as authorized. This is a security measure to prevent your server from becoming an "open relay" for spammers. Common Causes [SOLVED] Zimbra 9 SMTP relay authentication The error in Zimbra typically occurs when the
Let’s move from theory to practice. Below are the leading reasons this error appears in production environments.