Microsoft Exchange Server Logon problem

This is a problem happened before.  After over two weeks of back and forth with IT, it was resolved by deleting the Outlook client profile and start setting up the mail account again.

It came up again two weeks ago.  I removed the profile on two computers and it fixed the problem right away.  However, it came back occasionally. 

Symptom:
Outlook client log on error and asking for password again even though the originally saved password is correct.  Entering the correct password again won't work. 

This only happened on one computer while other computers with Outlook or other e-mail clients (e.g. iOS) worked fine.  However, this problem will eventually cycle through other devices as well.  In most times, it will go away after cancel the logon box. 

Solution:
It seems that the authentication encryption may be the cause:
https://support.microsoft.com/en-ca/help/3032395/outlook-connection-issues-with-exchange-mailboxes-because-of-the-rpc-e

In my case, the encryption was already enabled.  I just changed the "logon network security option" from  "negotiate authentication" to "password authentication (NTLM)". 

Then it worked.  After checking the setting again, it went back to "negotiate authentication".  It seems that the change in this setting reset a faulty state.