"more than 1 match was found" when trying to resolve a recipient mail user in OWA.
Everything seems setup correctly but when sending email from outlook you gets NDR with the error message
"#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##"
And when search the same user in owa you get notification that "more then one match found", this seems strange as when you search AD or adsiedit you don't find any duplicate and neither it's a cache issues.
Well fix was pretty simple to apply EAP check uncheck the
"Automatically update email address based on email address policy"
You can do this from the EMC or using Powershell for Mailuser.
Set-MailUser –identity testuser1 – EmailAddressPolicyEnabled:$true
Set-MailUser –identity testuser1 – EmailAddressPolicyEnabled:$false