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
- SMTP Header/banner reports "220 smtp.example.com ESMTP Symantec Messaging Gateway"
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