How to Fix Outlook Not Connecting to Microsoft 365 (Modern Auth & Credential Fix)
Is your desktop Outlook client stuck on Disconnected or constantly asking for password credentials? Follow these 4 proven methods to restore your Microsoft 365 connection.
Step-by-Step Video Walkthrough Watch on YouTube ↗
Common Symptoms and Quick Fixes
| Symptom | Likely Cause | Quick Fix |
|---|---|---|
| Outlook prompts for Basic Auth popup | Modern Authentication disabled or blocked | Enforce OAuth2 via Registry / Modern Auth |
| Stuck on Disconnected after a password change | Expired cached token in Credential Manager | Clear cached Microsoft credentials |
| Cannot find server during profile setup | Autodiscover CNAME missing or wrong | Verify autodiscover CNAME points to outlook.com |
Method 1: Clear Cached Microsoft Credentials in Windows
Windows Credential Manager stores encrypted OAuth tokens. When an expired token gets locked, Outlook enters an endless silent authentication loop.
1
Close Outlook and all related appsMake sure outlook.exe, teams.exe and onedrive.exe are closed. Check Task Manager for background processes.
2
Open Windows Credential ManagerPress Win + R, type control keymgr.dll and press Enter. Open the Windows Credentials tab.
3
Remove MicrosoftOffice16 and ADAL tokensUnder Generic Credentials remove entries starting with MicrosoftOffice16_Data:, MS.Outlook.15: and adal_token. Then restart Outlook.
Pro Tip for AdministratorsOn domain-joined PCs, also run klist purge in an elevated prompt before reopening Outlook.
Method 2: Enable Modern Authentication via Registry
Run this in Command Prompt as the affected user, then restart Outlook.
reg add HKCU\Software\Microsoft\Office\16.0\Common\Identity /v EnableADAL /t REG_DWORD /d 1 /f
reg add HKCU\Software\Microsoft\Office\16.0\Common\Identity /v Version /t REG_DWORD /d 1 /f
reg add HKCU\Software\Microsoft\Exchange /v AlwaysUseMSOAuthForAutoDiscover /t REG_DWORD /d 1 /fMethod 3: Verify the Autodiscover CNAME
Run the check below. The result must point to autodiscover.outlook.com.
nslookup -type=cname autodiscover.yourdomain.com4
Fix the DNS recordIn your DNS host create CNAME autodiscover pointing to autodiscover.outlook.com, then wait for the TTL to expire.
Method 4: Create a Clean Outlook Profile
If a corrupted profile is the cause, a new one fixes it without touching your mailbox.
5
Open Mail settingsControl Panel > Mail (Microsoft Outlook) > Show Profiles > Add.
6
Set the new profile as defaultAdd your Microsoft 365 account, choose Always use this profile, then reopen Outlook.
Frequently Asked Questions (FAQ)
Q: Will deleting credentials in Credential Manager delete my emails or OST files?
No. It only removes cached login tokens. Your mailbox data on Microsoft 365 is untouched.
Q: Is the registry change safe?
Yes. These keys only enable Modern Authentication, which Microsoft 365 requires. Export the key first if you prefer.