Outlook crashes or freezes on large attachments
Usually the mailbox cache is the culprit, not Outlook itself. Shrinking or relocating usually helps within ten minutes.
Try this first
- 1Fully quit Outlook, wait a minute, and reopen. Not just minimise, force-close via Task Manager.
- 2Check if the attachment is larger than ~30 MB. Exchange Online defaults to 35 MB, admins can raise it up to 150 MB, and many receiving mail servers cap lower. Send via a OneDrive link instead.
- 3Shrink your OST cache: File > Account Settings > set "Cached Exchange Mode" to 1 year instead of "All".
- 4Start Outlook in Safe Mode (Windows key+R, "outlook.exe /safe"). Does it open fine? Then an add-in is the problem.
When to bring us in
If Outlook also crashes in Safe Mode, or several colleagues are hitting it simultaneously, it is not a local issue. That is when we should look at it.
See also
- Teams: they cannot hear me, or I hear nothingIn our experience Teams usually picked the wrong audio device after a Windows update or a new headset.
- OneDrive has stopped syncingThe cloud icon is grey or has a warning. Locally changed files are not showing up for colleagues.
- A SharePoint file is held by someone for hoursThe lock persists long after the colleague closed it. Nobody else can edit.
None of the above fits?
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