Exchange 2013 - random NDRs for two accounts

Hello!

Have some more issues with our Exchange environment.

We have two email accounts (users), who are not getting all the emails. I have multiple people reporting NDRs when emailing them so I am sure that a "poisoned Outlook cache" could not be a problem. It does not happen all the time so I wonder if that could be specific to one of our three servers which are part of our DAG that happens to process the message. These are the last two accounts that I remember creating as well. No other users are generating NDRs.

There were more than one variants of the message so far and those were as follows:

Remote Server returned '550 5.1.1 RESOLVER.ADR.RecipNotFound; not found'

Remote Server returned '554 5.2.0 STOREDRV.Deliver.Exception:ObjectNotFoundException; Failed to process message due to a permanent exception with message The Active Directory user wasn't found. ObjectNotFoundException: The Active Directory user wasn't found. [Stage: CreateSession]'

Remote Server returned '532 5.3.2 STOREDRV.Deliver; Missing or bad StoreDriver MDB properties'
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rr2rAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
An RODC will not cause this issue but i would recommend that you remove any DC's from your environment if they are not being used and or removed from the domain.

The only reason why i suggested check your DC's is that Exchange references Active Directory and if Exchange is referencing one DC and it works and then references another DC and it does not work you might have a USN Roll back issue with your DC's.

In that case it is not Exchange it is Active Directory. Have you been able to try my other suggesting using OWA?

Will.
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matrix8086Commented:
this two accounts, was deleted and recreated, or moved from a datastore to another?

I rather guessing that they have been deleted and recreated, and some other users use the autocomplete option when type their email addresses, and the autocomplete points to the old ID which was deleted.

When you create an user it receives a SID which is unique. If you delete and recreate a username, it is a total different user account, even if the username is the same

Ask the senders who receive this error, to write the email address of those two users until the end, not to use the autocomplete function. I am pretty sure that it will works with no problems

Best regards!
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rr2rAuthor Commented:
Matrix:

Those were not re-creates to the best of my knowledge. Odd thing is for one of those an automated email system also generates NDRs (so there is no cache at all in that case). I will be looking for more clues...
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matrix8086Commented:
If you have a big infrastructure with more than one datastore, check how the message routing works for those users
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rr2rAuthor Commented:
Matrix:

One of them has no issues. The other person reported at least once case with the following error (while emailing a user who has no knows issues on his own):

This message could not be sent. Try sending the message again later, or contact your network administrator. The client operation failed. Error is [0x8004010f-0x8004010f-0x000501].
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matrix8086Commented:
I am afraid that you have a problem with the datastore. A consistency problem ... Check the logs!
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Will SzymkowskiSenior Solution ArchitectCommented:
What about your active directory replication? Is this working correctly? Use the following below commands...
repadmin /replsum
repadmin /showrepl
repadmin /bridgeheads
DCDiag /v

Have you tried logged into OWA and sending an email from there? This would determine if it was a caching issue or not. Also have you been able to move these mailboxes to another database and then test again?

Will.
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rr2rAuthor Commented:
Matrix:

If I understand correctly, such inconsistency would come up during backups? We are not seeing any errors during our daily backups of Exchange though.

Will:

Hmm.... We have a single Read-only DC that sits at a remote site, which was offline for a long time. That one is out of sync now. Did not even think about that server as a possible cause, however, that one should not be used by client here in corporate. I will investigate that approach.
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rr2rAuthor Commented:
repadmin /replsum does not look "clean" at all - going to work at this in more detail..
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rr2rAuthor Commented:
@Will

Although your points did not fix the NDR issues, they pointed me towards the issue with the "tombstoned" DC. I did try to migrate one of the affected mailboxes and got the "Forrest not up to date" error. Upon further investigation I got a solid report that the 5th DC is the root cause - it fails the replication checks. I will need to address that situation before I can work on the NDR issues - and quite possibly those might be gone once the replication works OK again.

I shall open a separate ticket under the Active Directory section shortly.
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