Microsoft confirmed that the issue was resolve and we continued monitoring to ensure there were no further issues. A restart of Outlook is recommended. Here is the official update from Microsoft.
"We've finished the deployment of our fix and we've confirmed via monitoring and user reports that the issue has been mitigated. Users will be required to restart their applications for the changes to take effect. Please reference EX255650 for further details."
We are closing this Incident at this time.
Posted May 12, 2021 - 07:03 CDT
Here is the most recent update from Microsoft:
"The deployment of our fix is progressing as expected and we continue to anticipate that it'll complete on Wednesday, May 12, 2021 by 3:00 AM UTC."
Posted May 11, 2021 - 21:18 CDT
This update from Microsoft:
"We’ve identified the root cause and are applying a fix, which will reach affected users over the next 3 to 4 hours. Users will need to restart the Outlook client to apply the fix after it's received. We expect to restore service to affected users by May 12, 2021, at 3:00 AM UTC."
We'll continue watching for updates from Microsoft as they work to resolve this issue.
Posted May 11, 2021 - 20:08 CDT
Microsoft is investigating an issue with email message visibility in Outlook. Outlook on the web appears to be unaffected. More details can be found under EX255650 in the MS admin app - https://aka.ms/M365AdminMobile or on their official Twitter Feed at https://twitter.com/MSFT365Status. EMPIST will continue to monitor and provide updates as they are available.