Exchange Email Routing Intermitten Issue

Hello all,

I have an environment with 3 exchange servers. 2 of them have CA, MBX and HT roles, and 2 databases in 1 DAG. The other one is the Witness Server, only running HT role. This is all running on Windows 2008R2.
I recently migrated from another exchange forest in order to fix the internal domain name which was setup incorrectly as a single label domain name.
Everything is working well currently, except that once in a while, a user using OWA will email a distribution group and the email will bounce back with a #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## error. If the user tries again the next second, it will go through. Upon checking out the bounce message I can see that the name of the distro group is not being resolved correctly and it displays the legacyExchangeDN name.
I don't understand why that happens when using OWA, which means they are not using any cache and I don't understand why this happens one second, but the next second it resolves correctly. Can anyone help?
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amenezes0617Asked:
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Beyond Next SolutionsSolutions ArchitectCommented:
I've run into something similar before. Look at the ProxyAddresses attribute of that distribution group, and see if that legacyExchangeDN is listed as a proxy address of that group. If not, add it. You can use ADUC in Advanced view to access the attribute editor tab of the dist group, or ADSI Edit, or get-distributiongroup.
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amenezes0617Author Commented:
It's not listed, but when I look at the old DC, it's not there either. And none of my groups have that either. Do you know why it looks for it one time and not another?
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Beyond Next SolutionsSolutions ArchitectCommented:
Users' personal contacts (outside of the GAL). Also, do you have any public folders with shared contacts? If so, and users have outlook configured to resolve there before the GAL or personal contacts I've seen both cause the issue.
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amenezes0617Author Commented:
I don't have shared contacts in our PFs. But what I don't understand is that both times this happened when the user was using OWA to send the email.
I will try adding the legacy name as you recommended and see if it helps, however I probably won't know if it really worked or not for a while as this only happens once in a while.

Thanks for help though.
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Beyond Next SolutionsSolutions ArchitectCommented:
If you have it narrowed down to one specific user, try searching the user's entire mailbox (including subfolders) for the legacy DN. See what that turns up in Outlook and through OWA.
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amenezes0617Author Commented:
No, it's happened 3 times, all from different users... that's too bad.

Thanks a lot.
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Beyond Next SolutionsSolutions ArchitectCommented:
OK, so if I understand correctly, the problem is sporadic and 3 users have reported the error when sending to this one particular distribution group. You also stated you performed a cross-forest Exchange migration- was this distribution group also migrated? Sounds like it was. So, under these assumptions, you have 2 options:

1. (Preferred) Ensure that all proxy addresses of the original distribution group from the source forest have been copied exactly to the migrated distribution group's proxy addresses field in the destination forest, including SMTP, CC Mail, X.500, etc...all of them.

2. You could try to simply delete and recreate the distribution group and manually re-populate the members. I haven't tried this method to resolve this issue, but I don't see any reason it wouldn't work.

Let me know how it goes!
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amenezes0617Author Commented:
Well, the problem is not specific to one group, or one user. It happens intermittently to several groups and people. However I was comparing the groups attributes in the old domain and in the new one and neither one has that legacy name in the proxy field. I don't mind updating AD but if the old one doesn't have the legacy name there why would the new one need it? And why would it work one time and not another?
I'm just a little confused. Thanks for your help.
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amenezes0617Author Commented:
Ok, i did some more digging and found that the name that shows on the error of the bounce messages, is the OLD legacyDN name and that the groups in the new domain have the NEW legacyDN name.
So the question is, why is exchange looking for the OLD legacyDN? Sometimes only?
Specially when we're using OWA to send out the emails? This must be in our GAL somewhere?
This information is in the legacyExchangeDN field. Not the proxyAddresses field.

Any ideas?
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Beyond Next SolutionsSolutions ArchitectCommented:
As for why stuff is looking at the legacy DN at all is a question for MS...I asked them that very same thing!  As long as you take the legacyExchangeDN from the source object and add it as a proxyAddress on the destination object the problem should clear up (after updating the address book with the new info, which you can do via: get-addressbook|update-addressbook). May not have the exact command right, going off memory.

IIRC, the prepare-moverequest.ps1 script is supposed to take care of that.

Hope this helps!
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amenezes0617Author Commented:
Thanks. I will try that.
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amenezes0617Author Commented:
So far so good, I tried this on the most used group and haven't gotten a complaint yet, i think it might have fixed it. Thanks for your help.
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Beyond Next SolutionsSolutions ArchitectCommented:
Rock on!
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