Reverse DNS checks fail, causing sent messages to not be delivered through Symantec Messaging Gateway (SMG). You may also see errors referring to a reverse DNS mismatch.

This issue is caused by mismatching DNS records or hostname on Messaging Gateway. When a DNS reverse (PTR) record returns a different name than the forward (A) record returns, or which appears in the Messaging Gateway SMTP banner's hostname.

Example of records that could cause this issue:

• MX lookup for example.com returns mail.example.com
• Forward DNS (A) lookup for mail.example.com returns 192.0.2.25. The reverse DNS (PTR) lookup for 192.0.2.25 returns name mail1.example.com
• SMTP Header/banner reports "220 smtp.example.com ESMTP Symantec Messaging Gateway"

• Verify that the SMTP banner hostname matches that of the MX, A, and PTR record.
• Check if Messaging Gateway is set to accept messages for multiple domains. In this case there may be several DNS MX and A records configured that direct mail to the Messaging Gateway for the domains, causing DNS mismatch errors or delivery issues.
• Direct each of the domains to common MX records for a single hostname and PTR address, which will resolve DNS mismatches.

Examples:

• Messaging Gateway accepting messages for: example.com, example.net
• MX lookup for example.com returns mail.example.com
• MX lookup for example.net returns mail.example.com
• IP (A) lookup for mail.example.com returns 192.0.2.25 and the reverse (PTR) lookup for 192.0.2.25 returns mail.example.com
• SMTP banner returns "220 mail.example.com ESMTP Messaging Gateway"

To change the name reported in the SMTP greeting banner

1. In the SMG Control Center, navigate to Administration > Configuration.
2. Select the scanner being changed, and click SMTP > Advanced Settings.
3. Change the "MTA host name:" field. and then click Continue.
4. Click Save.