Microsoft Solutions

Hi I recently go the following Error and thought I would let you know how I resolved it:

ERROR:
5.1.1 Unknown User - when sending an Email from outside our orginization to a known new user inside my orginization.

So what I did is I ran the following in "Exchange Management Shell" on my CAS/HUB server.

Test-EdgeSynchronization -VerifyRecipient user@domain.com

And received the following output at the bottum next to Revipient Status:

NotSynchronized - More than one recipient found in target Edge Server and may cause NDR on Edge server. RecipientStatus.ConflictObjects contains relevant entries.

CAUSE:
There was multiple CredentialRecords and CookieRecords for the specific user.

RESOLUTION:

Run the following to Force a Sync to your Edge:

Start-EdgeSynchronization -ForceFullSync

This resolved my problem, hope it can help you as well.