We were tasked to resolve a peculiar error for a client who was trying to generate some new rules in their Exchange Environment. The user was getting “There are multiple recipients matching the identity “<user>”. Please specify a unique value.”. This was being generated if either you tried to create a rule via Outlook on Web (formerly OWA) or by using Exchange Management Shell.
We discovered that the problem occurs if multiple mailboxes or mail contacts have the same display name. Exchange examines the Display name field or the displayNameattribute when it creates a rule.
You can resolve this by simply changing the display name in the Exchange admin center or in Active Directory Users and Computers so that the name doesn’t conflict with an existing mailbox or mail contact.
