Outlook asks for password when updating address book
If the user logs into one box and it seems to accept it and then a different box pops up then likely as others have said, clear related credentials from user credentials and be sure they're using the correct username especially if they use their email address UPN.probably not the same issue but I had a similar problem with dovecot where the client reached the maximum number of imap connections allowed per ip account and outlook kept asking for the account password, this was because the server certificate changed and android clogged the number of connections since it wouldn't automatically accept the new certificateso if you can, maybe try to check the exchange logs Check the 'remember my credentials' when entering in their password next time the box appears.
Once we have added the exchange server IP/DNS name to "bypass proxy server for local addresses" in IE or whatever browser they are using the problem was gone.The problem “Microsoft Outlook 2016 for Mac keeps asking for password” has been around for since March of 2016.Microsoft should have addressed this issue a long time ago with a patch. Just empty the whole thing out is what I do usually. Every time I used to empty it was in an enterprise environment with a domain where the vault wasn't required anyway, because it should have just used currently logged on credentials. You have two options: a.) Go to the user, close Outlook. b.) if a.) doesn't work, close Outlook, open the Control Panel, look for Credential Manager, check for Windows Credentials. Where would you point me to learn more and try identify potential causes (it is known to affect users with no VPN access, so I don't think that's the cause). This can have multiple reasons but most of the time it's a user changing his password while connected over VPN. Many of our users get this exact issue after changing their password, and clearing the password vault is the workaround/solution.
This solves the problem, up until they have to change their password, then we just repeat the process.