You’re working on an email reply when your screen goes blank. “Microsoft Outlook is not responding.” You wait, the screen comes back, and you keep working on your emails. Twenty minutes later, the same thing happens again. The third time it happens, you compose your emails using a two-step process: write the draft and save it in Notepad, then copy and paste the result into Outlook to send.
Repeated Outlook crashes are often the result of one of a small number of causes. Here’s the checklist we use.
First: which Outlook are you running?
Microsoft ships two different Outlooks. If your title bar or the toggle in the top corner says “New Outlook”, you’re on the newer app. Most of this troubleshooting advice won’t apply. This post is about Classic Outlook — the desktop program many businesses still run.
1. Install updates before anything else
Many crashes are the result of known bugs that Microsoft has already fixed. In Outlook, go to File → Office Account → Update Options → Update Now and let it finish. If Outlook won’t stay open long enough, update from another Office app like Word — they share the same updates.
If the crashing started right after an update rather than before one, a bad patch could be the cause. Microsoft often fixes those quickly. Either way, be current with your updates before you troubleshoot anything else.
2. Test in safe mode — it’s often an add-in
Add-ins are the most common cause of repeated Outlook crashes — they connect Outlook to your phone system, CRM, meeting scheduler, or PDF tool.
Close Outlook, press Windows key + R, type outlook.exe /safe, and press Enter. Safe mode starts Outlook without add-ins. Use it that way for a while. If the crashing stops, you’ve found your gremlin: go to File → Options → Add-ins, choose COM Add-ins → Go, untick everything, then re-enable add-ins one at a time — restarting Outlook after each — until the crash comes back. The last one you enabled is your culprit. This is Microsoft’s own first step for resolving Outlook crashes, and in our experience it works more than half the time.
3. Repair Office
If safe mode still crashes, the Office installation itself may be damaged. Close all Office apps, open Settings → Apps → Installed apps, find Microsoft 365, choose Modify, and run a repair. Try Quick Repair first — it takes a few minutes and fixes corrupted files locally. If that doesn’t help, run Online Repair, which reinstalls Office properly. Plan for that to take a while.
4. Rebuild the local mailbox file
Classic Outlook keeps a local copy of your mailbox in an OST file, and a corrupted OST causes this kind of repeated crashing. If your email is in Microsoft 365, the file can be safely rebuilt from Microsoft’s online servers: close Outlook, open File Explorer, and paste %localappdata%\Microsoft\Outlook into the address bar. If you don’t see .ost at the end of the filename, that’s normal — Windows hides known extensions by default; look for a file named after your email address, or check the Type column for “Outlook Data File.” Rename that file by adding .old to the end. Reopen Outlook and it downloads a fresh copy. On a large mailbox this can take a few hours to re-sync, so do it at the end of the day, not before an important send.
5. Create a new Outlook profile
Your profile holds account setup and settings, and it can quietly become corrupted after a failed update or a hard shutdown. Open Control Panel → Mail → Show Profiles → Add, set up your account in the new profile, and set it as the default. If Outlook runs fine there, delete the old profile.
A note about the old advice
If you’re following an older guide that says “download Microsoft’s Support and Recovery Assistant (SaRA)” — that tool is gone. Microsoft retired SaRA in March 2026 and folded its diagnostics into the Get Help app built into Windows. If a guide’s screenshots show that same tool, the rest of its advice may be dated too.
When it’s not Outlook
If you’ve run through the whole list and Outlook still crashes, the problem is typically something other than just Outlook: a machine that’s struggling generally, a drive that’s failing, or a mailbox that’s grown too large for the machine to reliably cache. Those are worth diagnosing properly rather than applying endless patches.
If you’d rather not deal with the headache yourself, hand this off — we’ve dealt with this many times. In most cases, it’s an afternoon to fix, not a project that lasts for days. Book a call and we’ll take it from there.
