Hi,

We have Exchange 2013 installed, and we receive emails sent from external senders normally. However, if an email is sent to a number of addresses, but one address is wrong, then server rejects complete email (nobody receives ) with response 550 5.1.1 User unknown.

Thank you for any help

I don't believe that is normal behavior for Exchange 2013.  Do you have any message hygiene appliances or services between the Internet and Exchange?

Hi,

We use Exchange Online Protection for message hygiene, but I can see in receive connector logs that message is entering server. I don't know how Exchange Online Protection and Mail Server communicate in this aspect.

• Edited by Qaku 42 minutes ago