Migrated user mailbox was disabled on-premises

Occasional Contributor



I hope someone can help me with this.  We have exchange 2010 and Office 365 hybrid environment.

This problem is related to user termination. 

When we disable a user account using on-prem ad of a user with a mailbox in Office365, Office 365 move mailbox to 'Deleted users'. Therefore, If I send an email to this email address I get a bounced back mesaage saying mail address is no longer valid.


To overcome this

I renamed ex-employees email address to a different email address using on-prem exchange console.

Then, I added this terminates user's email address to the user's manager's mail account as an alias. I added this alias using the on-prem exchange console as Office365 doesn't allow to add the alias due to it is syncing with the on-prem ad(1.jpg). 


When I ran full sync between Azure ad and on-prem, I get dir Sync errors.


"We detected a duplicate Proxy address conflict on the value smtp:ABC.def@comapny.com.au. All attribute values need to be unique across objects. To resolve this conflict, first determine which object should be using the conflicting value. Then, update or remove the conflicting value from the other object(s). "



I really appreciate if someone can help me with fixing this.





3 Replies

Simply disabling the account in AD will not cause it to be deleted in O365, you are most likely moving it to a different OU or otherwise excluding it from the DirSync scope. So the first question here is do you actually intend to delete the user (and its mailbox) from Office 365 or?



Hi Vasil,

Thanks for the reply. You are correct. We are moving disabled users to a different OU. I want to delete these account permanently . But I need a way to forward these email address to a current user.


Once you move them to a new OU, you have to wait for dyrsync to run a cycle or two and synchronize the changes fully to O365, then you should be able to re-use the SMTP addresses. Also make sure that the mailbox is not put on hold in O365, as this will prevent it from being deleted and cause conflicts.