I am currently migrating from exchange server 2010 to 2016. The first step in my migration path is to get all exchange 2010 servers to exchange 2010 sp3 . I have created the exchange server with service pack 3 and I am now migrating users to this new server.
A test user that I have migrated is able to receive mail both internally and externally , send internally but when they send externally they get a mail protection bounce back error from outlook .
Any ideas ?