Changing email addresses for migrated distribution lists…

When a distribution list is migrated the cloud only list has attributes that are fully managed in Exchange Online. This allows all attributes including the primary SMTP address associated with the group to be changed in Exchange Online.

If the distribution list has been migrated with the -enableHybridMailFlow switch or had enable-hybridMailFlowPostMigration run this results in mail flow objects existing in both Active Directory and Exchange Online. It would be possible for the primary SMTP address to be updated in Exchange Online and hybrid mail flow being broken as a result.

When hybrid mail flow is enabled a dynamic distribution list holds the same primary SMTP address as the migrated distribution list. In order for relay or other Exchange on-premises functions to continue to work the address would need to be updated in both directories. 

Version 2.9.8.26 now enables a command update-HybridMailAddress. This command allows an administrator to specify a new primary SMTP address and alias for a migrated distribution group. The command searches Active Directory to locate the dynamic distribution list created and if found the Exchange Online primary SMTP address is updated. If the primary SMTP address can successfully be updated in Exchange Online the primary SMTP address and mail address of the dynamic distribution list is updated in Active Directory. Changing the alias is optional, and if specified when changing the primary SMTP address the alias is updated in both Exchange Online and Active Directory.

Having a single command ensures that hybrid mail flow works when processing a primary SMTP proxy change.