Password popups due to Microsoft changing the office 365 authentication method.

Some users are reporting a persistent password popup in their mail application this morning, this is due to Microsoft changing the Microsoft/Office 365 authentication method and requiring 'modern authentication' by default.

If you are using Outlook 2013 this can easily be solved by changing\adding a Registry setting in Windows which is normal and 'IT support level' change:

(more details here https://learn.microsoft.com/en-gb/microsoft-365/enterprise/modern-auth-for-office-2013-and-2016?view=o365-worldwide)

This can also be easily pushed out by 'group policy' if you have a Windows domain.

If you're seeing this in another mail app for example on your phone this will require further investigation and planning.

Alternatively, some authentication methods can be turned back on again but Microsoft has made this change to improve security.

Here is some further reading on the subject:
https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-deprecation-in-exchange-online-september/ba-p/3609437