A new Microsoft Security Update is being rolled out to Hosted Exchange to secure a new zero-day vulnerability. Microsoft states the update could impact the following short term:

1. Search errors in Outlook Desktop: Microsoft has linked an article regarding this error and provided registry change fixes to resolve the issue - Search error in Outlook cached mode after installing March 2024 SU - Microsoft Support

2. Users may be unable to preview certain Office attachments via OWA – Microsoft is working on releasing a patch

3. Read vs Unread message indications may be inconsistent via Outlook Desktop – Microsoft is working on releasing a patch