Email account will not authenticate in this computer only - Outlook O365

[Rigo]

Hello folks
Fighting an account that cannot be successfully authenticated whether IMAP or POP3 but only on one computer.
This is a company with their own domain .com.au hosted on third party servers.
No problem connecting to that account from any other computer.
But the troublesome computer has no problems with setting up other accounts either, there are two other ones happily working on IMAP from the same hosting.
I've tried through Control Panel - User Accounts - Mail, it won't authenticate
I've tried directly through Outlook, no success.
Repaired the Office installation, checked whether an old pst/ost file might be around that could confuse the setup, none found.
Temporarily disable AVG IS, just in case.
Now considering complete Clean re-install of Office, if that doesn't work
Nuke n pave the whole thing - a bit drastic to access one email account only?
What could be lurking in that computer against that particular account?
Where to look for the blockage and get rid of it?

 

[carmen617]

First of all, I would remove AVG completely, but that's just me, can't stand that program. Secondly, have you tried creating a new profile in Outlook? If that doesn't work, try creating a new user account on the system and see if it will authenticate there.

 

[Markverhyden]

Have you checked event viewer to see what it says? I'd also try to engage the hosting company support to see if they can shed any light on whats happening. Have you tried to create a new profile on the computer and then add the account?

 

[nlinecomputers]

Time to bring in SaRA.

Download Microsoft Support and Recovery Assistant from Official Microsoft Download Center

SaRA is a desktop client that enables Microsoft customers to troubleshoot and diagnose their issues

www.microsoft.com

 

[Sky-Knight]

IMAP / POP3, and AVG is installed?

@carmen617 is right! AVG is the problem. You cannot "disable" that thing... remove it, reboot and watch your problem vanish. I can all but guarantee you it's the ancient pop3/imap proxy that mess comes with borking things up. Let Defender do its job, ditch the "Free" garbage AV.

 

[Rigo]

I would remove AVG completely

I did think about it but somehow didn't go through with it.
Will do it next and see
Thanks

 

[Rigo]

Have you checked event viewer to see

Not quite sure what I should be looking for in there. Really grateful for some pointers

 

[Rigo]

Time to bring in SaRA.

Download Microsoft Support and Recovery Assistant from Official Microsoft Download Center

SaRA is a desktop client that enables Microsoft customers to troubleshoot and diagnose their issues

www.microsoft.com

Thank you for the utility, have downloaded and will give it a spin.
If not for this case, definitely in the toolbox

 

[Rigo]

ditch the "Free" garbage AV

It's the full pro version but I don't think that makes any difference

 

[Metanis]

As of this morning my own personal Outlook.com account would no longer allow me to login using an alias. I had to use the credentials for the primary account. Probably totally unrelated to the OP's issue but I thought I'd toss it out there as perhaps something has changed on the Microsoft authentication side of things?