Outlook Won’t Open? Fixes for Classic, New Outlook, Mac and Mobile

When Outlook won’t open, the problem is almost always on that one device: an add-in that crashes at startup, a damaged mail profile, a corrupt local data file or a broken Office install. Your mailbox itself is usually fine.

The fastest way to tell is to check your mail somewhere else. Sign in to Outlook on the web (outlook.office.com for a work account, outlook.com for a personal one) or open mail on your phone. If everything is there, the mailbox is intact and the fix is on the computer. Two exceptions: mail kept only in .pst files on the PC never shows up online, and plans such as Microsoft 365 Business Basic don’t include desktop Outlook at all. If the web version fails too, it’s an account or service problem, and reinstalling Outlook won’t help.

Then work out which Outlook you’re running, because the startup fixes differ completely by version.

Which Outlook do you have?

Several different apps are called Outlook, and a fix for one does nothing for another. Safe mode, mail profiles and data-file repair exist only in classic Outlook; the new Outlook for Windows runs on Microsoft Edge WebView2 and doesn’t load COM add-ins.

If Outlook won’t open far enough to show the toggle, check the Start menu. Classic Outlook (version 2407 and later) is listed as Outlook (classic). Since early 2025 the new app is listed simply as Outlook; PCs that haven’t updated may still show Outlook (new).

Classic Outlook: fix it in this order

1. Make sure Outlook isn’t already running

Right-click Start, choose Task Manager, select Microsoft Outlook and click End task. A hidden copy that never finished closing blocks a new one from starting.

2. Run Microsoft’s startup troubleshooter

Microsoft 365 business customers can run Microsoft’s automated startup troubleshooter. On Microsoft Support’s Classic Outlook troubleshooters page, select Start under the startup troubleshooter, then Open when the browser asks to open Get Help.

3. Start in safe mode to test add-ins

Press Windows key + R, type outlook.exe /safe and click OK. Safe mode skips COM add-ins and toolbar customizations, so if Outlook opens now, an add-in is almost certainly the cause.

1. In safe mode, go to File > Options > Add-ins.
2. Next to Manage: COM Add-ins, click Go.
3. Note which boxes are ticked, clear all of them and click OK. Don’t click Remove; that deletes the add-in instead of disabling it.
4. Close Outlook and open it normally. If it works, turn add-ins back on one at a time, restarting Outlook each time, until the problem comes back.

The usual suspects are third-party add-ins for PDF tools, CRMs, phone systems, e-signature and antivirus email scanning. If it’s your antivirus’s add-in, disable only the add-in, never the antivirus, then update it; on a company PC, tell whoever manages security.

If Windows says it can’t find outlook.exe, use the full path in quotes. On most Microsoft 365 installs that’s "C:\Program Files\Microsoft Office\root\Office16\outlook.exe" /safe, or the same path under Program Files (x86) for 32-bit Office.

4. Update Office and Windows

If Outlook opens even briefly, go to File > Office Account > Update Options > Update Now. If it doesn’t, run the same update from Word or Excel; Office updates as one package. Then install pending Windows updates and restart.

5. Reset the folder pane

If Outlook starts and then stops with “Cannot start Microsoft Outlook. Cannot open the Outlook window,” close it and run outlook.exe /resetnavpane. That switch clears and rebuilds the folder pane for the current profile. You lose custom favorites in the folder pane, not email.

Stuck on "Loading Profile" or "Processing"

A splash screen that never gets past Loading Profile or Processing means Outlook can’t finish reading the mail profile or the data file behind it. Try these after safe mode, because a bad add-in can cause the same hang.

Create a new mail profile

The profile holds your account settings, and a damaged one is a common reason Outlook hangs at startup. Creating a new profile doesn’t touch the mailbox on the server.

1. Close Outlook. Open Control Panel, search for Mail and open Mail (Microsoft Outlook).
2. Click Show Profiles > Add, give the profile a name and sign in with your email address.
3. Select Prompt for a profile to be used so you can switch back if needed, then click OK.
4. Start Outlook and choose the new profile.

If the new profile works, keep it. Before removing the old one, note where its .pst files are, such as old archives or POP mail: in the same Mail dialog, select the old profile, click Properties > Data Files. You can then open those files in the new profile. If the old profile has an IMAP account, its calendar and contacts exist only on this PC, in folders marked (This computer only); move them into a .pst first, because removing the old profile deletes them.

Rebuild or repair the data file

Microsoft 365, Exchange and Outlook.com accounts keep mail on the server, and Outlook stores a local copy in an .ost file. You don’t need to repair that file. Close Outlook, find it with the Open File Location button on the Data Files tab, rename it (for example to name.ost.old) and reopen Outlook. Outlook recreates it and downloads the mailbox again; you lose only items that never synced, such as a message stuck in the Outbox. IMAP accounts use an .ost too, but their calendar and contacts live only in that file, so move those into a .pst before you rename it.

For .pst files (POP accounts and archives), copy the file somewhere safe first, then run the Inbox Repair tool, SCANPST.EXE. On most current installs it’s in C:\Program Files\Microsoft Office\root\Office16, or the same folder under Program Files (x86) for 32-bit Office. Run it again until it reports no errors.

Check for redirected folders

Microsoft lists an AppData folder redirected to a slow network share as a cause of Outlook hangs. If only users with redirected folders are affected, that’s a Group Policy fix for whoever manages your network.

Outlook opens, then keeps crashing

When Outlook crashes instead of hanging, Windows records what failed. Open Event Viewer, go to Windows Logs > Application, choose Filter Current Log and enter 1000. Open the Outlook entries and read the Faulting module name.

To repair Office in Windows 11, right-click Start > Installed apps, find your Microsoft 365 or Office entry, click the … menu and choose Modify. Run Quick Repair first. If that doesn’t help, run Online Repair, which takes longer and needs an internet connection. In Windows 10 the same option is under Apps and Features.

Outlook opens but keeps showing Not Responding

Check the status bar first: AutoArchive or a phone syncing with Outlook can tie it up, so let that task finish. If it freezes in one large folder, move older mail into subfolders or an archive. Outdated antivirus that plugs into Outlook is another documented cause, so update it. If the whole PC freezes, see why a computer keeps freezing.

The new Outlook for Windows won’t open

The new Outlook is a Microsoft Store app with no safe mode, Control Panel profile or data-file repair, so the fix list is short.

1. End the task. Right-click Start > Task Manager, select Outlook, click End task, then reopen it.
2. Restart the PC and install pending updates. The new Outlook and the WebView2 runtime it runs on update themselves in the background.
3. Repair the app. Right-click Start > Installed apps, search for Outlook and find the new Outlook (plain Outlook on updated PCs, Outlook (new) on PCs that haven’t updated). Click the … menu > Advanced options > Repair. Repair keeps the app’s data.
4. Reset it if Repair doesn’t help. On the same page, choose Reset. Microsoft says Reset deletes the app’s data, so you’ll add your accounts again, and anything stored only in the app on this PC can be lost.
5. Uninstall and reinstall. On the same Advanced options page, select Uninstall. Then search for Outlook in the Microsoft Store app, choose Get and sign back in.

If the new Outlook says it isn’t compatible with the current service, it has missed updates. Microsoft’s fix is to close and reopen the app so it can apply the latest one.

Outlook for Mac and the Outlook mobile app

On a Mac, install updates first with Help > Check for Updates (Microsoft AutoUpdate), then restart the Mac. With a Microsoft 365 account, turn off any Legacy Outlook switch; legacy Outlook for Mac stops connecting to those mailboxes starting October 2026. If Outlook still won’t start, test a fresh profile:

1. Quit Outlook. In Finder, open Applications, right-click Microsoft Outlook and choose Show Package Contents.
2. Open Contents > SharedSupport > Outlook Profile Manager.
3. Create a new profile, make it the default and open Outlook.

Don’t delete the old profile until the new one works: that deletes all mail and data stored in it on the Mac, and only server-based accounts such as Microsoft 365 download again.

On iPhone or Android, update the Outlook mobile app, force-close it and reopen it. If it still crashes, delete and reinstall it; mail lives on the server, so nothing is lost. Phones managed by your company may also need a broker app (Microsoft Authenticator on iPhone, Intune Company Portal on Android) or an app PIN before Outlook will open.

When several people can’t open Outlook: admin checks

Two or more broken PCs at once usually means a shared cause, so check these before touching individual machines.

• Service health. In the Microsoft 365 admin center, open Health > Service health and look for Exchange Online or Microsoft 365 apps incidents.
• Licenses. Under Users > Active users, confirm each affected user still has a license that includes the desktop apps.
• Recent changes. An add-in deployed from the admin center, a Group Policy or Intune change, or an Office update that landed the same day is the likeliest shared cause.
• Sign-in loops. If Outlook opens but keeps asking for a password or shows Disconnected, it’s an authentication or connection issue. See our guides to email authentication errors and Outlook disconnected from the server.

If you’d rather have someone else handle the Microsoft 365 side, such as adding and removing users, password resets and security setup, see Microsoft 365 management.

When to stop and get help

• Outlook hangs along with other apps and the disk is constantly busy. The drive may be failing or overloaded; see 100% disk usage in Windows.
• Your .pst file is very large, stored on a network drive or kept inside OneDrive. Those setups cause repeated hangs and need a planned move, not another repair.
• SCANPST keeps finding errors after several runs, or the .pst is your only copy of years of mail. Copy it before doing anything else.
• Everyone’s Outlook broke at the same time and service health is clear.

If you’d rather not do this yourself, Outlook not opening on a single PC is a typical $59 remote fix: with your permission, a technician connects through our remote computer help and works through add-ins, the profile and the data file while you watch, and you can end the session at any time.

Common questions

How do I reset Outlook to default settings?

Classic Outlook has no single reset button. The closest thing is a new mail profile, which rebuilds the account settings without touching mail stored on the server. Running outlook.exe /resetnavpane resets the folder pane, and outlook.exe /cleanviews restores default views but deletes any custom views. The new Outlook has a real Reset under its Advanced options in Installed apps; it deletes the app’s data, so try Repair first.

Will creating a new mail profile in Outlook delete my email?

Creating one deletes nothing. For Microsoft 365, Exchange and Outlook.com accounts, everything lives on the server and downloads again into the new profile, which can take a while for a large mailbox. IMAP mail downloads again too, but Outlook keeps IMAP calendars and contacts only on the PC, in folders marked This computer only. Move those into a .pst, and note where any POP mail or archive .pst files are, before removing the old profile.

How do I start Outlook in safe mode in Windows 11?

Close Outlook, press Windows key + R, type outlook.exe /safe and press Enter, then choose your profile if asked. You can also hold Ctrl while clicking the Outlook icon and confirm the safe mode prompt. This only applies to classic Outlook; the new Outlook for Windows has no safe mode because it doesn’t load COM add-ins.

Is it safe to delete the Outlook OST file?

For Microsoft 365, Exchange and Outlook.com accounts, yes. The .ost is a local copy of a server mailbox, and Microsoft says Outlook recreates it the next time it opens. Rename it rather than deleting it, and expect to lose anything that never synced, like a message stuck in the Outbox. IMAP accounts are different: their calendar and contacts live only in that .ost. Never treat a .pst file this way; it may be your only copy.

Outlook won’t open after a Windows or Office update. What should I do?

Restart once more so the update can finish, then try safe mode. If several people are affected at the same moment, check Service health in the Microsoft 365 admin center and Microsoft’s page of recent classic Outlook issues, which lists known update bugs with their fix status and any workaround. Running Quick Repair, then Online Repair, from Installed apps fixes many damaged installs.

Why does my email work on my phone when Outlook won’t open on my computer?

Because the mailbox lives on the server and only the computer’s copy of Outlook is broken. Your phone and Outlook on the web connect directly to the same mailbox, so mail stored there is safe. The exception is POP mail or archives kept only in .pst files on the PC, so copy those before repairing anything. Focus on the PC: running processes, add-ins, the mail profile, the local data file and the Office install, in that order.