Rejected message by MTA

Products

• Messaging Gateway

Issue/Introduction

Emails from a specific sender are having the Action on Message Audit Logs as: Rejected Message by MTA without any other information

When looking on Message Audit Logs we can se the entry:

2023 Feb 16 08:17:41 +04 (warning) ecelerity: [22298] LUA: RDNS: RDNS lookup for connecting IP x.x.x.x returned SERVFAIL 
2023 Feb 16 08:17:41 +04 (debug) ecelerity: [22298] scriptlet-00340: lua_resume returned 0 
2023 Feb 16 08:17:41 +04 (info) ecelerity: [22298] ML-REJECT: Rejection on: x.x.x.x:x, sent to host: x.x.x.x:x, Audit ID Not Available, 421 4.4.0 Unable to connect to DNS - try again later#015

Performing a reverse lookup with any DNS server configured on SMG returns SERVFAIL

Environment

Release: 10.7.3

DNS validation enabled on SMG (Protocols > Settings > SMTP)

Cause

The sender IP address does not resolve to any DNS record on the DNS servers.

Resolution

Sender needs to fix his DNS records