This problem occurs because the OU property of the user contains an incorrectly escaped forward slash. For example, if "My OU/" is the name of the OU, "My OU\/" would be the properly escaped version. Passing "My OU\/" to Get-UserPrincipalNamesSuffix would let the cmdlet run correctly. However, "My OU/" is instead passed to Get-UserPrincipalNamesSuffix. In this situation, the cmdlet fails and returns the error message that is mentioned in the "Symptoms" section.
Workaround 1Use the Exchange Management Shell to manage the affected user accounts.
Workaround 2Avoid the use of OUs that contain forward slashes in their names when you store users and groups that will be used by Microsoft Exchange Server.
Article ID: 3173169 - Last Review: Jun 27, 2016 - Revision: 1