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 10.10.10.25. The reverse DNS (PTR) lookup for 10.10.10.25 returns name mail1.example.com
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.