Mailing List Message #104527
From: Urs Grützner <>
Subject: Weird DNS Problem
Date: Thu, 17 Oct 2013 10:06:19 +0200
To: CommuniGate Pro Discussions <>
X-Mailer: Apple Mail (2.1084)
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
2010051792 ; serial
10800      ; refresh (3 hours)
3600       ; retry (1 hour)
604800     ; expire (1 week)
3600       ; minimum (1 hour)
) 3600 IN A 124266 IN A 124266 IN A 94849 IN A 94849 IN A

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