I have migrated most of my mailboxes from our Exchange 2010 server to our Exchange 2013 server. (single Exchange 2010 server (all roles) and a single Exchange 2013 server (all roles) within the same domain.
Two of my users have started seeing their x500 address show up as their return address and show up as the creator of Calendar meetings on their computers (Outlook 2010, Outlook 2013). From OWA, they see their user name, and the recipients of their emails or calendar invites see their username and or email address (SMTP). But from their own outlook they see their x500 address. The strangest part, is that even after deleting the x500 address from their user mailbox in Exchange 2013 ECP they still see this address. Also, If the user is not in cached mode, the x500 does not appear.
So, I guessed that it was a profile issue and creating a new profile for the user would fix the problem. I created a new profile and it did fix the problem, for 1 day, then the issue returned. Where is Outlook getting the address from? It is no longer an address for the user. And if the user is not in cached mode, the issue does not occur.
So far it is not causing any mail flow issues, just annoyance with end users.
Note: Exchange 2013 is in hybrid configuration with Exchange Online and the x500 address /0=ExchangeLabs/... is still present, but it is not the x500 address that is showing up for the users.
Fred Zilz