By default, whenever you create a mailbox in your Exchange infrastructure, the primary email address for the mailbox is being assigned based on the email address policy applied to the user. Recently, I have been working with a customer for Exchange 2010 hybrid implementation with Office 365 and we ran into an issue of email address being changed after the mailbox is migrated to Office 365. Primary email address of mailboxes being migrated to Office 365 from on-premises Exchange 2010 had been changed. You will notice this issue in your hybrid implementation if you have more than one email address policy applied in your exchange organization.
Understanding Email Address Policy
From the behavior of email address, it was obvious it’s being done by email address policy but the question is which email address policy and why? As we are running infrastructure in a hybrid mode and our on-premises infrastructure is the source of authority so we need to look into Exchange 2010 email address policies to fix the issue.
If you have more than 1 email address policy in your Exchange organization than It’s recommended to review your email address policies before moving any mailbox to Office 365.
In my scenario, i had 2 email address policies configured on Exchange 2010 as shown below.
For those of you who don’t know why we need to create another email address policy, In Exchange 2010, you cannot modify the criteria and conditions of default email address policy that’s why organizations tend to create a new custom policy as per their requirements. Default email address policy assign an email address of email@example.com with a scope of “All Recipient Types“.
The custom email address policy was configured to be applied on “Users with Exchange Mailboxes” and the primary email address was configured as first initial and last name (e.g. firstname.lastname@example.org)
Why Email Address was changed?
We understand the email address policy configuration, now whenever a mailbox is migrated to Exchange Online the Default Policy will be applied to the mailbox instead of the custom policy because the custom policy scope is set to only “User Mailbox” and when you move a mailbox to Office 365, it converts the mailbox to MEU and our custom policy was not applied to MEU. As a result, the default reply address is set to riaz@instead of what might have been originally intended.
How to Fix It?
Now, we understand the problem and it’s time to fix the issue. We have 2 options to fix this issue.
- Modify the Custom Policy to apply to all Recipient Type
- Modify your default email address policy to add additional SMTP address matching the custom policy and set the email address as primary address
Once you apply the fix, you need to wait for Azure AD connect sync to happen to replicate the changes to Office 365. Hope this article help you fix your issue with incorrect email address applied to user mailbox after the mailbox is migrated to Office 365.