Hello,
I have received "550 5.1.1 User unknown" error when I send mail from external mail (such as gmail) to my one of users. (user1@contoso.com)
This problem exists only in one user. Everything is okay with other users.
After uncheck "Block messages sent to recipients that do not exist in the directory" on Recipient Filtering on the "Edge Transport Server" my problem is solved.
My Question is:
if the user (user1@contoso.com) exists in my AD then why I received "550 5.1.1 User unknown" error?
Why I should uncheck "Block messages sent to recipients that do not exist in the directory"?
I don't want to uncheck that settings.
My Environment:
Two Mailbox Server (Exchange 2013 CU13);
One Edge Transport Server (Exchange Server 2010);
I have installed Anti-spam and anti-malware on Mailbox servers.
Thank you for your help...