Error [#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##] "more than 1 match was found" when trying to resolve a recipient mail user in OWA

Everything seems to be setup correctly, but when sending an email from Outlook, the user gets NDR with the below error message Exception.

"#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##"

And when you searched the same user in OWA, you gets a notification, that "more than one match found".

This seems strange as when you search in Active Directory or do an LDAP search using adsiedit tool, you don't find any duplicate recipient, and neither it's a cache issue.

Well fix was pretty simple and just needed to check un-check EAP settings.

"Automatically update email address based on email address policy"

You can do this from the EMC or use Powershell for Mailuser.

Set-MailUser –identity testuser1 – EmailAddressPolicyEnabled:$true

Set-MailUser –identity testuser1 – EmailAddressPolicyEnabled:$false