Mircosoft Outlook crashes at startup on Mac

Question

My Microsoft Outlook app (on Mac) doesn't open anymore. It immediately crashes on startup

Mac version: 26.3.1

Outlook version: 16.107.1

I also can't open it in Safe mode (holding option key)

Any help would be appreciated.

Answer 1

On macOS, Outlook startup crashes are commonly tied either to a known calendar bug in older builds or to general Outlook/Mac stability issues.

Given Outlook 16.107.1 and that it crashes immediately (even when trying safe mode), use these steps:

1. Update Outlook and macOS

• There is a known issue where Outlook for Mac crashes on startup or during mail sync when a calendar event has a NULL OriginalStart property. This was fixed in Outlook version 16.47 and later.
• Even though the current version is newer than 16.47, ensuring both macOS and Office are fully up to date is the first step:
  • In Outlook for Mac (if it opens long enough) go to Help > Check for Updates to launch Microsoft AutoUpdate and install all available updates.
  • If Outlook will not stay open at all, open any other Office app (Word, Excel, PowerPoint) and use Help > Check for Updates there.
  • Also update macOS via System Settings > General > Software Update or via the Apple guidance at https://support.apple.com/en-us/HT201475.

2. If crashes persist, reinstall Office and reset Outlook data If Outlook and other Office apps are unstable, a clean reinstall plus profile/data reset is often required:

• Quit all Office apps.
• In Finder > Applications, Command+click all Microsoft 365/Office apps (Outlook, Word, Excel, PowerPoint, OneNote) and Move to Trash.
• In Finder, use Go > Go to Folder… and open:
  • ~/Library/Containers/
  • Delete folders starting with:
    • com.microsoft.Outlook
    • (optionally also com.microsoft.Word, com.microsoft.Excel, com.microsoft.Powerpoint, com.microsoft.OneNote if other apps are also crashing).
• Go back to ~/Library and open Group Containers and move to Trash (if present):
  • UBF8T346G9.ms
  • UBF8T346G9.Office
• Empty the Trash.
• Sign in to the Microsoft account dashboard and reinstall Office/Outlook from the account’s services page.

3. If Outlook still crashes on startup

• After reinstall and data reset, if Outlook still crashes immediately, use Outlook on the web temporarily while continuing to keep Office and macOS updated, as recommended for the calendar crash issue.
• If the problem is tied to a specific calendar item (NULL OriginalStart), using Outlook on the web to review and delete any obviously corrupt or “stuck” calendar entries may also help once the client can start.

If none of the above resolves the issue, collect crash logs from Console.app and contact Microsoft Support, referencing that Outlook for Mac crashes at startup even after full reinstall and profile reset.

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References:

• Outlook for Mac crashes unexpectedly on startup or during mail synchronization
• Fix for Outlook for Mac stability issues
• Microsoft Office apps for Mac quit unexpectedly - Microsoft Q&A
• Can't access Microsoft support - Microsoft Q&A