Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may be unable to sync or send new email messages from Outlook for Mac – RESOLVED
25/11/2024 09:02:00 AM
NHSmail Reference: INC47053645
Microsoft Reference: EX937987
Issue Status: RESOLVED
Issue Description: Some users may be unable to sync or send new email messages from Outlook for Mac.
More info: Impact is specific to users leveraging the new Outlook for Mac client version who have session-based, strict location conditional access evaluation policies applied.
This issue potentially affects those who installed Current Channel (Preview) builds starting from 16.91.24110320 and Current Channel builds starting from 16.91.24111020 who have enforced continuous access evaluation (CAE) policies.
The fix is slated for deployment in the next 16.92.* builds, slated to deploy to Preview on December 3, 2024 and then to Current Channel on December 10, 2024.
Users who have CAE enforced through their tenant should refrain from upgrading to the above 16.91.* builds and wait for 16.92 rollout which will have the fix.
For users already in these builds hitting this issue and that can opt in to the Beta Channel, the latest Beta build already has the fix. Please follow the instructions on the following link to get to Beta channel:
For those who are unable to leverage the Beta Channel build, users can restart Outlook to get back to a syncing state. However, the issue might reoccur after few hours into session.
Users can also install the 16.90.24110120 build from the previous month to avoid this issue. However, this may cause a resync of Outlook when launching for the first time.
Final Update: 05/12/2024 08:10:00 AM – Microsoft have deployed a fix for all builds 16.91.1110.0 onwards, and, after monitoring to ensure service health has returned to acceptable thresholds, they’ve verified impact has been remediated.
Scope of impact: This issue only affects users that are leveraging the new Outlook for Mac client who have session-based, strict location conditional access evaluation policies applied.
Root cause: A recent service update to a portion of the Outlook for Mac service infrastructure contains a code regression, resulting in users” claims challenges being rejected when attempting to authenticate into their mailbox.
Next steps: Microsoft are continuing to investigate the recent service update to determine what caused this issue to occur in order to improve our service update practices to ensure this issue doesn’t happen again.
