Mailing List Message #104528
From: Brian Turnbow <>
Subject: R: Weird DNS Problem
Date: Thu, 17 Oct 2013 09:17:01 +0000
To: 'CommuniGate Pro Discussions' <>



SMTP is for outgoing sessions SMTPI for incoming sessions, so your server is saying it received an error message from the remote server.

If you filter for  SMTP-023132 you can see the full session ( depending on debug levels)

As it is send a 451 “temporary” error Communigate will try and resend the message  every  xxx until it times out  after yyy depending on your smtp settings.







Brian Turnbow
Network Manager

TWT S.p.A.


Da: CommuniGate Pro Discussions [] Per conto di Urs Grützner
Inviato: giovedě 17 ottobre 2013 10:06
A: CommuniGate Pro Discussions
Oggetto: Weird DNS Problem


CGP 5.1.16 on Mac OS.X.5.8




We have a set up where mails to some of our users at are forwarded to another server



By coincidence I see in the queue, that a mail is not being forwarded since 2 days with the following log entry: 


09:35:49.970 1 SMTP-023132( [5249863] return-path rejected, got:451 4.1.8 Sender address <> domain does not resolve  




When I make a look up the domain however HAS a IN MX entry.

I have also verified that the DNS entries in the mail server System are correct, from our provider Swisscom,   





- What does the log entry mean, which SMTP rejects? is it the sending SMTP ( or is it the receiving SMTP ( which cannot resolve the domain ?

- What happens when a forwarding finally  fails? Does the original sender get a Undelivery message? 



Thanks for help







; <<>> DiG 9.6-ESV-R4-P3 <<>> any +multiline +nocomments +nocmd +noquestion +nostats +search

;; global options: +cmd        3600 IN      TXT "v=spf1 mx ptr ip4: ip4: ?all"        3600 IN      MX 10        3600 IN      SOA (

                          2010051792 ; serial

                          10800      ; refresh (3 hours)

                          3600       ; retry (1 hour)

                          604800     ; expire (1 week)

                          3600       ; minimum (1 hour)

                          )        3600 IN      A        3600 IN      NS        3600 IN      NS        3600 IN      NS        3600 IN      NS           124266 IN A           124266 IN A           94849 IN A           94849 IN A


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