When sending an inbound message to a Messaging Gateway, the peer gets an error response of "421 4.4.0 Unable to connect to DNS - try again later"
Similar error messages to those below are found in the maillog:
2011 Jun 29 10:34:12 HKT (warning) ecelerity:  sieve: RDNS: RDNS lookup for connecting IP 126.96.36.199 returned SERVFAIL
2011 Jun 29 10:34:12 HKT (info) ecelerity:  ML-REJECT: Rejection on: 188.8.131.52:25,200, sent to host: 184.108.40.206:49653, Audit ID 01010109-b7c6dae000005a92-01-4e0a8f2485e6, 421 4.4.0 Unable to connect to DNS - try again later
2011 Jun 29 10:34:12 HKT (notice) ecelerity:  ESMTP-02739
2011 Jun 29 10:34:12 HKT (info) ecelerity:  ML-HOST_DISCONNECTED: 220.127.116.11:49653 disconnected. (ID 90656f58)
This issue can occur when you enable any of the DNS Validation features under Potocol > Settings, and there are problems with the configured DNS server(s).
Ensure that the configured DNS server is working, and is not overloaded. Navigate to Administration > Configuration > host > DNS/Time.
Imported Document ID: TECH163486
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