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2017-07-27 11:20:25 1dZoIA-0003hY-Oi == email@target-domain.com R=dnslookup defer (-1): host lookup did not complete
2017-07-27 11:20:25 1dafu5-0001k3-LG <= <> R=1dZoIA-0003hY-Oi U=Debian-exim P=local S=1201 T="Warning: message 1dZoIA-0003hY-Oi delayed 48 hours"
2017-07-27 11:20:41 1dafuD-0001k6-NO DKIM: d=sending-domain.com s=default c=simple/simple a=rsa-sha256 [verification succeeded]
2017-07-27 11:20:41 1dafuD-0001k6-NO <= <> H=localhost (mail.sending-domain.com) [127.0.0.1]:55325 I=[127.0.0.1]:10025 P=esmtp S=1938 id=E1dafu5-0001k3-LG@mail.sending-domain.com T="Warning: message 1dZoIA-0003hY-Oi delayed 48 hours"
2017-07-27 11:20:41 1dafuD-0001k6-NO ** email@sending-domain.com: Unknown user
2017-07-27 11:20:41 1dafuD-0001k6-NO Frozen (delivery error message)
2017-07-27 11:20:41 1dafu5-0001k3-LG => email@sending-domain.com R=dkimproxy T=dkimproxy_smtp H=localhost [127.0.0.1]:10027 DT=16s
2017-07-27 11:20:41 1dafu5-0001k3-LG Completed

I have replaced the domain names and email addresses from that log. I am trying to work out what is happening.

It seems like the bounce message is frozen. When I manually (using the command line) send an email to the bounce address, it arrives. But in this particular case we are using Sendblaster to send messages to our clients.

I don't understand why 1dafuD-0001k6-NO is frozen but 1dafu5-0001k3-LG is completed.

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The message with the ID 1dafu5-0001k3-LG, is an ordinary local delivery:

R=dkimproxy T=dkimproxy_smtp H=localhost [127.0.0.1]:10027

, where the original address is given in angle brackets after the final delivery address. This is basically a bounce back notification, that let's you know that your DNS fails to resolve the MX entry of target-domain.com .

The 2nd message, that has the ID 1dafuD-0001k6-NO has been routed via an intermediate address:

H=localhost (mail.sending-domain.com) [127.0.0.1]:55325

, where the R and T fields represent the router (R) and that transport (T) that were used to process the address. This messaged failed to be delivred, as it wasn't able to find a mailbox associated with email@sending-domain.com (as we know that this exists, the intermediate address returned this message).

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  • "This messaged failed to be delivred, as it wasn't able to find a mailbox associated with email@sending-domain.com" - Thanks for all that useful information. How can this problem be resolved? That email address does exist.
    – I Newton
    Jul 28 '17 at 12:48
  • The receiving system may think you are sending spam an refusing delivery. There are other reasons why delivery may be temporarily suspended. It looks like the message timed out on the queue, so the assumption is the user does not exist. Read the bounce message(s).
    – BillThor
    Jul 28 '17 at 13:32

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