Messages not delivered due to reverse DNS mismatch

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Article ID: 157354

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Updated On:

Products

Messaging Gateway

Issue/Introduction

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.

Cause

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"

Resolution

  • 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, demo.org
  • MX lookup for example.com returns mail.example.com
  • MX lookup for example.net returns mail.example.com
  • MX lookup for demo.org returns mail.example.com
  • IP (A) lookup for mail.example.com returns 10.10.10.25 and the reverse (PTR) lookup for 10.10.10.25 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.