Outlook Cannot Connect to Server

Windows 10 - Ver: 21H2 - Build: 19044.2130

Microsoft 365 - Ver: 2210 - Build 16.0.15726.20070) 64-bit

Some years ago I had added a work Microsoft 365 email account to Outlook 365, setup as IMAP via ' Control Panel > Mail (Microsoft Outlook) > Account Settings > Add'):

Incoming Server: Outlook.office3365.com - Port: 993 - Security: SSL/TLS - Requires Authentication

Outgoing Server: smtp.office365.com - Port: 587 - Security: STARTTLS - Requires Authentication

All has been OK since, until recently...

Randomly, the work email account didn't connect to the Microsoft Exchange Server. Over a few days, this problem has progressed to permanent; I.E. the work email account no longer connects to the Microsoft Exchange Server.

I am able to access the work email (and any of the Microsoft 365 apps) by logging on to the work Microsoft 365 account via a web browser.

I have Nine other email accounts setup locally in Outlook 365, all of which connect to their respective mail server on booting Outlook 365, some of which are Microsoft Accounts.

To investigate/remedy this problem, I have caried out steps:

• Check the email setup via ' Control Panel > Mail (Microsoft Outlook) > Account Settings > Change'). If I click Next the 'Test Account Settings' box opens - Confirmation fails quickly, followed by the 'Internet Email [account name]' username and password confirmation box, seeking confirmation of settings keyed in at time of setting up the email account.
• Confirmed with our work Administrators the Microsoft 365 account shows no faults regarding my Microsoft 365/Exchange email account.
• Confirmed with our work Administrators Adanced Security is NOT setup (Two-Step Authentication and App Passwords).
• Change the Microsoft 365 Password (in the work Microsoft 365 account AND my local email setup).
• Remove ALL Add-ins.
• Remove and (attempt to) Re-Add the work email account.
• Remove and Create a New Profile for Outlook 365, followed by (attempt to) Re-Add the work email account.
• Boot Outlook 365 in Safe Mode and (attempt to) Re-Add the work email account via 'Outlook > File > Account Settings > Account Settings > New'.
• Uninstall/Reinstall Microsoft 365. (I have setup all nine of the other email accounts in Outlook 365 via ' Control Panel > Mail (Microsoft Outlook) > Account Settings > Add').
• Only the work email account presents the problem of failing to connect to the Exchange Server.

Any assistance in resolving this matter most welcome.

Best Regards

C