Legacy Outlook for Mac users may be unable to connect to their Exchange Online mailboxes

Title: Legacy Outlook for Mac users may be unable to connect to their Exchange Online mailboxes

User impact: Legacy Outlook for Mac users may be unable to connect to their Exchange Online mailboxes.

More info: Impact is specific to those who are on version 15.20 and builds 7409.15 or below. As the fix progresses throughout our safe deployment processes, admins can check if they’re on builds 7409.16 or above to validate if they’ve received the fix or not by running the following cmdlet:

Get-Mailbox TestUser | fl *version*

The cmdlet produces an “AdminDisplayVersion” output which delineates which version a user is on.

Current status: As we continue to monitor the fix deployment, we’ve assessed that the deployment process is taking longer than originally anticipated. We expect the aforementioned process to be completed by our next scheduled update.

Scope of impact: Users on the legacy Outlook for Mac client that’s on version 15.20 and builds 7409.15 or below may be impacted.

Start time: Friday, March 15, 2024, at 8:00 AM UTC

Estimated time to resolve: We expect the deployment process to be completed by Friday, March 22, 2024, at 10:00 PM UTC.

Root cause: A recent service maintenance change introduced a code issue that inhibits communication between legacy Outlook for Mac users and the Exchange Online service, which is resulting in the impact.

Next update by: Friday, March 22, 2024, at 10:00 PM UTC