Hi i am getting the error below when sending an email to an external mail contact from our on premise Exchange Server. Emails sent to this recipient from gmail etc work fine.
There is a problem with the recipient's e-mail system. More than one user has this e-mail address. The recipient's system administrator will have to fix this. Microsoft Exchange will not try to redeliver this message for you. Please provide the following diagnostic text to your system administrator and then try resending the message after the problem has been resolved.