Outlook 2016 doesn't accept password or app password

Struggled for hours to get a connection last night. Got it. But today, it's back to ceaseless password prompts.

MS execs are really earning their $112M+ compensation packages, aren't they? May the billionaire class get what they deserve one day soon.

I have the same problem for 1 week....been running Office 2016 for 8 years on Windows 10 and 3 yrs on Windows 11 and never a problem with authentication unless I changed the password. This is a fix Microsoft has to make. Its so annoying you could be browsing or working on a word document and the password window pops up.

Gabriel, I am the CTO of Morgen Calendar, a calendar client that connects, among other things, to personal Outlook accounts and O365. Our users are also affected by this intermittent issue, even with an app-specific password.

Some technical info for your team.

• We are using EWS to fetch calendar info
• We have to use Basic authentication (email + password) because OAuth does not work for EWS on personal accounts. It works for O365 work accounts but not for personal Outlook accounts. Weird thing is, Apple Calendar is able to use OAuth with personal Outlook accounts, but nobody else using the EWS API can (meaning Busycal, Fantastical, etc.).

If we could switch to OAuth for these accounts, the problem would be solved for those clients that are willing to support modern authentication.

The main issue is with basic authentication. In order to mitigate my recommendation is to make OAuth work. I'm no expert on Thunderbird but I know it has support for OAuth. I found this article, Microsoft OAuth Authentication and Thunderbird in 2024 | Thunderbird Help (mozilla.org). Please try this configuration.

@Robdstef,

If you have M365 Personal the best experience would be to use the M365 Outlook that is part of your subscription. It connects with modern auth and is not affected by this recent issue. If you prefer Thunderbird, it would be best to follow the guidance of Thunderbird to use OAuth as noted in this article, Microsoft OAuth Authentication and Thunderbird in 2024 | Thunderbird Help (mozilla.org). I will keep sharing feedback to the service team to work on addressing the issues with basic auth, but you could skip all that with the other two options you have. Modern auth is also a more secure connection method so worth the effort to switch if you can.

This is, to the best of my knowledge, not true? I have this issue, and I'm running version 2401 (Build 17231.20194 CtR) with M365. The issue doesn't seem to be isolated to older builds.