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: