Exchange Online Writeback Keeps Cloud, Active Directory Mailbox Settings in Sync

Microsoft has made hybrid Exchange management easier with the general availability of Writeback for Cloud-Managed Remote Mailboxes in Exchange Online. The new capability enables administrators to manage mailbox attributes in the cloud while automatically synchronizing key changes back to on-premises Active Directory.

According to Microsoft, many organizations with hybrid Exchange environments still have mailbox identities tied to on-premises Active Directory, even as administrators increasingly prefer to manage Exchange settings in the cloud. This disconnect means that changes made in Exchange Online don’t automatically synchronize back to Active Directory. It creates inconsistencies for business applications that continue to rely on on-premises Exchange attributes.

Writeback keeps Exchange Online and Active Directory in sync

Microsoft’s new writeback capability addresses this issue by keeping key mailbox attributes synchronized between the cloud and Active Directory. It allows companies to modernize management without breaking existing systems.

“Writeback extends this capability by synchronizing a critical set of Exchange attribute changes from Exchange Online back to on-premises Active Directory through Microsoft Entra Cloud Sync. This helps organizations whose on-premises line-of-business applications continue to read Exchange attributes from Active Directory,” Microsoft explained.

Since its launch in public preview, Microsoft has increased support scale from 200,000 to 600,000 cloud-managed mailboxes per tenant, which makes the solution suitable for much larger environments. The company has also added support for writeback of the mail attribute, and changes to the mailbox email address in Exchange Online can now be synchronized back to Active Directory. The writeback feature now supports 24 Exchange-related attributes, including custom attributes, recipient type details, proxy addresses, and the mail attribute.

What administrators should know before enabling Writeback

Keep in mind that new writeback configurations created on or after August 3, 2026 automatically include mail attribute writeback. This means organizations that configured the feature during the public preview must update their attribute mappings to enable the new mail writeback capability. Microsoft advises that customers shouldn’t enable tenant-wide cloud management of Exchange attributes while mailbox migrations or recipient creation activities are still occurring on-premises.

Microsoft notes that the writeback feature is supported in commercial, GCC High, Department of Defense, and 21Vianet environments. If you’re interested, you can find more details about the prerequisites on this support page.