Changing the SMTP address on the O365 side with ADSync enabled

Question

Hello,

we need to make changes to ADDS ProxyAddress to add an alias to a mail user in Office 365.

The user is hosted in ADDS and synchronized with Entra via ADSync. However, it is very inconvenient to use the attribute editor in ADDS. But we cannot change ProxyAddress directly in Office 365.

Perhaps this is a problem due to the fact that once upon a time Exchange on-prem worked in hybrid mode. Currently only Exchange Online is used.

Please tell me how I can unlock the ability to change ProxyAddress in Office 365?

It is possible to ensure that ADSync does not use the hybrid Exchange option. Or is this a normal behavior for synchronized objects from ADDS?

Thank you.

Answer 1

Every configuration that involves AAD Connect/AAD Cloud sync requires that changes to the synchronized user objects are made in your on-premises AD. The only way to avoid that would be to disable synchronization altogether.

For the task at hand though, there is a workaround that you can leverage. You can use the Set-Mailbox cmdlet with the -WindowsEmailAddress parameter to "override" this behavior:

Set-Mailbox user@domain.com -WindowsEmailAddress new@domain.com

This adds new@domain.com as the Primary SMTP address for the user, while preserving the old Primary alias as secondary. However, this is not a supported method, and the changes you made might get overwritten on a full sync.