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Damian Gardner
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Corporate email is failing intermitently for one user when sending to recipients in other countries from the US

Hello - we have a corporate Exchange 2010 server with about 100 users.  One user is experiencing international email problems for the past couple weeks with email bouncing back to her.  She experiences no problems with domestic recipients, however.  It is also an intermittent issue - sometimes the message to an international recipient will work, while other times it is timing out.  This happens with multiple recipients from different domains, as well.  There appears to be no pattern, as of yet.  there have been multiple failures just this morning.  Not sure how to troubleshoot, but here is the common error between them:

1st MESSAGE:   mfavilli@uol.com.br (mfavilli@uol.com.br) <mailto:mfavilli@uol.com.br>
The server has tried to deliver this message, without success, and has stopped trying. Please try sending this message again. If the problem continues, contact your helpdesk.
#550 4.4.7 QUEUE.Expired; message expired ##

2nd MESSAGE:  contact@qedpackers.com
#554 5.4.4 SMTPSEND.DNS.NonExistentDomain; nonexistent domain ##

3rd MESSAGE:  稲垣慶三 (k.inagaki@lamerco.com) <mailto:k.inagaki@lamerco.com>
The server has tried to deliver this message, without success, and has stopped trying. Please try sending this message again. If the problem continues, contact your helpdesk.

Diagnostic information for administrators:
Generating server: EXCHANGE.lacoinc1.local
#550 4.4.7 QUEUE.Expired; message expired ##

4th MESSAGE:  Delivery is delayed to these recipients or groups:


Katherine <mailto:Katherine@sigma-medical.com.tw>

Subject: RE: po#20140521003 please pull in shipping schedule

This message hasn't been delivered yet. Delivery will continue to be attempted.
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Damian Gardner

8/22/2022 - Mon
Simon Butler (Sembee)

The location of the recipient shouldn't matter.
Do any others on the same server send to the same domains correctly?
Does the problem continue if used from OWA?

The messages are simply timeouts or queued messages, the NDRs are close to useless. You need to look in your queue viewer to see what is going on when the messages are queued.

Damian Gardner

Hi Simon - I don't know about other users sending, so I will try sending tests myself, as another user.  Didn't realize the NDRs are useless.  I'll watch the queue viewer then and report back what I see.  thank you
Damian Gardner

By the way - I assume I need to watch the queue AS the email is being sent, correct?  there's nothing logged in it? it's real time, I assume
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James Murphy
Simon Butler (Sembee)

The NDRs you have posted are timeouts. Therefore the message will be in the queue until the timeout has been reached - which is 48 hours by default. You don't need to watch it in real time.

However if the end user is getting back an immediately failure, then that can indicate a different problem.

Damian Gardner

Ok - so I did some tests and watched the queue.  For the first one on my list, it looks like the receiving server is doing a reverse lookup and it's not finding our hostname.  Here's the error:

Last Error: 450 4.7.1 Client host rejected: cannot find your hostname, []

The FQDN I have in my receive connector is EXCHANGE.LACOINC1.LOCAL, which I believe the server setup itself, on it's own.  Not sure how to be sure what it has to be to satisfy the reverse lookup.
Damian Gardner

well - from what I'm seeing, it has something to do with one of two things.  Based on the results from NSLookup when I check the IP address reported in the rejection notification in the message queue ( - which is the IP address of our ASA firewall gateway), it SEEMS like the FQDN the recipients server is looking for is the name of our OLD Exchange server from months ago (we migrated from "lacomail" to "exchange" server names early this year.  Strange thing is that nobody has complained about email trouble until just recently.  But the result of the NSLookup clearly shows that server name:

> set type=ptr
Server:  lacoad1.lacoinc1.local

Non-authoritative answer:      canonical name = 57.48/
57.48/        name = lacomail.laco.com

The OTHER thing it might be - and I'm not sure on this - is the rejection error from the recipient server states "cannot find your hostname"....which would be the actual name of our email server "EXCHANGE". Our DNS records show a PTR record for EXCHANGE =, which is it's own unique IP address, and this is the public address our email server has had for years.  the name was changed, as mentioned, from LACOMAIL to EXCHANGE about 8 months ago.  So - not sure if I need to change the EXCHANGE PTR record to match the .57 address, or what.

thanks for your help
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Simon Butler (Sembee)

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Damian Gardner

Sorry for the late response.  Let me check these two points, and let you know.

thanks Simon - I appreciate your help
Damian Gardner

Apologize for forgetting to check back.  We found it was a DNS problem with our server IP address.  Thank you for your help.