Outlook Not Working? Fix It by Symptom (Classic Outlook, Windows)

This page is about classic Outlook, not the new Outlook

Microsoft keeps two Outlook apps for Windows. Classic Outlook has File > Options, COM add-ins and profiles. The new Outlook for Windows does not, and its reset is simpler: end the task in Task Manager, uninstall from the Start menu, and reinstall from the Microsoft Store. It needs Windows 10 version 17763.0 or later.

Everything else here applies to classic Outlook 2013, 2016, 2019 and Outlook for Microsoft 365. Outlook for Mac has its own help and is not covered.

Symptom: Outlook freezes or says Not Responding

First, give it time. Check the status bar for background work such as auto-archive or a large attachment, and wait about 2 to 3 minutes. Then install pending Windows, Microsoft 365 and Office updates.

If it still hangs, press Win+R, type outlook.exe /safe and click OK. Accept the default profile if asked. Safe mode starts Outlook without add-ins, so if it works there, an add-in is the problem.

• Open File > Options > Add-ins, set Manage to COM Add-ins and click Go.
• Clear the checkboxes. Do not remove the add-ins. Click OK and restart Outlook.
• Turn add-ins back on one at a time, restarting after each, until the freeze returns.

Symptom: Disconnected, or Trying to connect, forever

Microsoft ties this status to a few different causes. Check the cheap ones first: Windows Update and a damaged profile are named as two of the most common causes of not sending or receiving. The free Support and Recovery Assistant (SaRA) for Microsoft 365 diagnoses and fixes common connection problems.

Two specific causes are documented. When IPv6 is on and your IPv6 network is faulty, Outlook shows Disconnected; the recommended fix is to repair the IPv6 network. The workaround is the registry value DisabledComponents, type REG_DWORD, set to 0xFF, under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters, or the option to prefer IPv4 over IPv6.

The second is an admin matter. A trailing space at the end of the legacyExchangeDN attribute produces Disconnected and the message that the .ost is not an Outlook data file. Only your Exchange admin can remove it with ADSIEdit.msc, and replies to old messages from that user may bounce afterward.

If several colleagues are affected, the admin should check the Microsoft 365 Service health status for Exchange Online before anyone changes settings.

Symptom: password asked every time, or Need Password in the status bar

This one has a precise cause. Outlook asks for the password on every start, or the status bar shows Need Password, when Office is not allowed to connect to online services. Creating a profile may fail too, with "Something went wrong".

Go to File > Options > Trust Center > Trust Center Settings > Privacy Options and tick the option that lets Office connect to online services from Microsoft. If it is greyed out, the registry value UseOnlineContent is 0. Under HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Internet, 0 blocks the option, 1 lets the user opt in and 2 (the default) allows it. The 16.0 folder covers Outlook 2016, 2019 and Microsoft 365; 15.0 is Outlook 2013. A value under the Policies key was set by Group Policy, so your admin must change it.

Symptom: mail sits in the Outbox until you press F9

Messages that go out only after a manual Send/Receive usually mean "Send immediately when connected" is off. Open File > Options > Advanced and turn it on in the Send and receive section.

The setting maps to the registry DWORD Send Mail Immediately under ...\Outlook\Options\Mail. A value of 0 means off. If the box is greyed out, Group Policy controls it, and you need your administrator to remove the policy.

A worked example: why a 25th mailing to 400 people bounces

Exchange Online limits are the cause of many "Outlook is not sending" reports. A mailbox may send to 10,000 recipients per day and 30 messages per minute. The recipient limit per message can be customized up to 1,000.

Say you send a club update to 400 recipients, one message at a time. After 25 messages you have reached 25 x 400 = 10,000 recipients, so the 26th message fails. Microsoft explains the reset: sending resumes only when the count of recipients over the past 24 hours drops below the limit. If you sent 5,000 at 09:00 and 5,000 at 11:00, you can send again at 09:00 the next day.

The size limits matter too. Microsoft lists 150 MB for a message and a single attachment in Outlook, 112 MB in Outlook on the web, and 33 MB in Outlook for iOS and Android. A message to a group of 5,000 to 99,999 members is capped at 25 MB, and at 5 MB for a group of 100,000. Size problems bring a non-delivery report rather than a frozen app.

Repairs in order: profile, data file, then Office

Microsoft's order for a stubborn problem is: create a new profile, repair the data file, then repair Office. To use a new profile, create it, hold Shift while starting Outlook and pick it in the Choose Profile dialog.

The Inbox Repair Tool, scanpst.exe, repairs a damaged data file. For Office itself, run Quick Repair first and Online Repair only if Quick Repair did not help. Online Repair is slower. Microsoft's repair pages returned an access error when I tried them on 2026-11-01, so this page does not give menu paths or file locations for those steps; use the Microsoft links in the sources.

Data files on a network drive cause freezes and corruption

Microsoft does not support .pst files on a LAN or WAN as a long-term setup. Write operations can take about four times longer than reads, and a weak connection can corrupt the file. Its fix is Cached Exchange Mode with a local Offline Folders file, or an Exchange or Microsoft 365 mailbox.

The one supported exception is Outlook 2010 or later hosted on a Windows Server 2008 R2 or later Remote Desktop Session Host, on a fast network, with one Outlook client per file. If your .pst sits on a network share and Outlook freezes, move it to the local drive first.

Common mistakes and who each fix suits

Removing add-ins instead of unticking them, which loses the settings. Reinstalling Office before trying safe mode. Editing the IPv6 registry key before fixing the network. Asking a home user to run ADSIEdit; that fix is for admins only.

If a message on the screen does not make sense, Crade can read it and explain what it means. Home users on a personal Microsoft 365 or POP/IMAP account can do all other steps themselves. Work accounts: policy-controlled boxes will stay greyed out, so ask your admin.