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Starting today all our company PCs with Outlook 2016 will no longer connect to Exchange Online (Office 365 account). When opening Outlook the user / pass prompt shows up. Submitting the username and password causes the prompt to reappear and Outlook will not start.

The Office 365 outlook web client and our mobile phones still work as expected...

I've tried deleting my local credentials, deleting outlook profile, online repair of office 365 install and running Microsoft support recovery (which shows all green check boxes).

All PCs are running Windows 10 build 1903. No Windows updates occurred last night.

"Exchange Health" in Office 365 administration is reporting no issues.

Results of Microsoft connectivity enter image description here

What are my next troubleshooting steps?

Thanks

payling
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3 Answers3

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Yesterday I was completing a few of Security & Compliance recommendations in Office 365...

One of those recommendations is called "Baseline policy: Block legacy authentication (Preview)"

The description for the policy is...

This policy blocks all sign-ins using legacy authentication protocols that don’t support multi-factor authentication (such as IMAP, POP, SMTP). The policy does not block Exchange ActiveSync.

Office 2013 (without registry keys), Office 2010, Thunderbird client, Legacy Skype for Business, Native Android mail client

I enabled this policy knowing I had no legacy applications installed on any PC. Boy was I wrong! Roughly 24 hours or so after enabling this is when Outlook 2016 decides to stop connecting to exchange. I disabled the policy and right away our Outlook 2016 clients could connect again!

What ... the ... heck!

I'll update once I figure out why Outlook 2016 is being effected

payling
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Since i can not add a comment

Have you checked two-factor auth enabled in O365?

Check it by temporarily (only while setting up the account in OL2016) disabling 2FA. Use the Microsoft diagnostic tool from here http://aka.ms/outlookconnectivity

Also what version of Office 2016 are you running on?

Uday Sriramadas
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  • Not sure how to find Outlook version. Opening outlook gets stuck at password prompt so I cannot reach "About". Outlook should be the latest build, updates are set to automatically download and install. Multifactor authentication is enabled only on admin accounts. Doesn't explain why non 2FA accounts will not work. Plus mobile phones and web clients work fine still. Diagnostic tool returns all green check marks. – payling Aug 27 '19 at 17:00
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I think you can check some registry entry such as HKEY_CURRENT_USER\Software\Microsoft\Exchange] “MapiHttpDisabled”=dword:00000001

Jayce
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