You ran a script to modify SMTP addresses on an Exchange 2010 user and accidentally overwrote all of their previous SMTP addresses including the legacyexchangeDN aka x500. (or you accidentally deleted a user and created their mailbox to the same AD account)
Now internal users are reporting that they’re receiving NDRs about the user no longer exists, even though you’ve already added the same exact SMTP address to their mailbox
Cause: Internal users typically caches the x500 address for internal communication instead of using SMTP addresses.
Not so efficient solution: Have every users that have this person’s contact autofilled in their Outlook client delete the contact from the autofill and re-enter their SMTP address.
Better: Have someone send a NDR to you for this particular user and recreate the x500 from that NDR on this user’s mailbox
Delivery has failed to these recipients or distribution lists:
The recipient’s e-mail address was not found in the recipient’s e-mail system. Microsoft Exchange will not try to redeliver this message for you. Please check the e-mail address and try resending this message, or provide the following diagnostic text to your system administrator.
If you click on the name, the NDR will get resolved to:
EXCH is the Exchange Organization name
So now we need to convert the above address into proper x500
First step: Replace all underscores “_” to “/”
Then replace all +28 to “(” and +29 to “)”
Replace all +20 to space ” ”
Replace all +2E to a period “.”
The final x500 would look like this:
/O=EXCH/OU=EXCHANGE ADMINISTRATIVE GROUP (28FHSDHJF23GHYED)/CN=RECIPIENTS/CN=P.Nguyen@PNLab.domainhere.com
Now just add this new string to the user’s Alias under the Exchange console as a custom address and you’re golden.