#550 4.4.7 QUEUE.Expired; message expired ##

We have a very important client who when they attempt to mail a user on our domain irregularly get's bounce backs with the message:

#550 4.4.7 QUEUE.Expired; message expired ##

The client in question does not appear to have issues mailing anyone else on our domain or any other. I receive all E-mail they send to me. The user here also has no other issues with his mail. As I said, the issue occurs irregularly: some days it's fine, others it's not.

Does anyone know if this is an issue our end or theirs please?
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Robin HumanHead of Network ServicesCommented:
Just before this it should give you the server that is providing the ndr - yours or theirs;
this normally indicates a routing or connector configuration error
Nick_SmithAuthor Commented:
The server named before this in the ndr is theirs.

To get more info, enable SMTP logging with full options and monitor these logs. Then you can see if your server contacts theirs and if so, what the answers are.
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Ask them to check the following:
  • Make sure their servers can resolve your Domain all the time
  • Make sure that from their server your MX records come out clean
Nick_SmithAuthor Commented:

Thanks for all your help. The problem is that the client is VIP, they are already vexed due to the mail situation and I really don't want to go back to them asking to check their end unless I've got some evidence to prove the case. Whilst the tips you've given are great, is there anything I can do from my end to prove the issue is theirs?
Enable SMTP logging and send some e-mails. Post the logs here.
See, since the NDR is being generated by their servers, it means there is no communication (in most cases). So major troubleshooting has to be done there
What you can do from your end is make sure that:
  • Send mails to yourself from various external domains and see if they are delivered properly
  • Make sure that any RBL that you might be subscribing to is not getting their Server IP / Domain off and on
Nick_SmithAuthor Commented:
turns out is an issue between their set up and our Ironport. They use a different host and subnet for outbound mail which doesn't have an A record, which causes the Ironport not to look favourably on it.

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Well, it amazes me that you said that we didnt resolve. WIthout access to your setup we can only point you towards issues and thats we did.
Also you do not respond for days.....Do not expect help from me atleast in future. Can't comment about other guys....
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