Outlook 2016 doesn't accept password or app password

I tried using Outlook 2021 to access my POP3 Outlook accounts and can confirm that it didn't fix the intermittent login issues.

I've decided to use Thunderbird, which works fine and looks a lot better than Outlook 2021 in my opinion. It was a bit of a faff migrating all my emails across (had to use an earlier version of TB for the conversion from the PST file and then upgrade to the latest version of TB) but I think it has been worth it.

With the way Microsoft seem to going I expect I will eventually have to move from Windows as well!

So, I use Office 2016, and of course Outlook 2016, which is not compatible with the new authorization rules. I have been struggling with this entire depreciation of older Outlook versions for a few months until Microsoft finally let us know what was happening.

I downloaded the "Outlook for Windows" App. It is eligible for the new authentication rules, and is free from the Microsoft store. It is certainly different, and does not seem to have all the features of Outlook 2016.

However, once I downloaded the "Outlook for Windows" app, and set up my outlook.com email in it, then the Outlook 2016 install settled right down. I am running both at the same time. My original thought is I would take some time to learn the new "Outlook for Windows" app, while still using my more familiar Outlook 2016 app.

So, to my surprise, so far at least, there have been no disconnects from authorization for my Outlook 2016 since installing and setting up the "Outlook for Windows" app. Not sure what is going on, but as the "Outlook for Windows" app authenticates my outlook.com email, the Outlook 2016 app flies under the radar. Maybe.

Anyway, I am letting the "Outlook for Windows" app just run in the background, and I am still happily using my Outlook 2016 app with no disconnects from authentication. For now, at least.

It doesn't matter if it's MSI or not. Only 2021 and later will support OAuth for the free MS email accounts.

So my version of Outlook that I installed will no longer support Basic Authentication? How do I know if it is an Outlook 2016 MSI version?

From: Modern Authentication Methods now needed to continue syncing Outlook Email in non-Microsoft email apps

https://support.microsoft.com/en-us/office/modern-authentication-methods-now-needed-to-continue-syncing-outlook-email-in-non-microsoft-email-apps-c5d65390-9676-4763-b41f-d7986499a90d

If you use Outlook for Windows: 

Outlook supports Modern Authentication in all current Microsoft 365 subscription SKUs and Outlook 2021 LTSC (any SKU with build 11601.10000 or higher) when connecting directly as Outlook.com. If your Outlook is configured to connect to Outlook.com using POP or IMAP, Modern Authentication is not supported. This means that when Basic Authentication is fully deprecated, it will no longer connect.  For this scenario, you have a few options:

Option 1: Get a newer Outlook email app which supports Modern Authentication

If your Outlook client does not support Modern Authentication, you will need to upgrade to the latest version and then setup using Outlook.com Sync. You can either purchase a new Outlook License, use the Outlook that is included in your Microsoft 365 subscription, or download Outlook for Windows for free.  

Option 2: Switch to Outlook.com/Exchange Syncing

Instead of using POP/IMAP and SMTP, create a new Outlook Desktop profile and then add your Outlook.com account using automatic account configuration, which will add the account with Modern Authentication. To do this, please use the following guidance:

1. Create a new Outlook Desktop profile. For more information, please go to Create an Outlook profile.
2. Add your Outlook.com account. For more information, please go to Add an email account to Outlook.

The following versions of Outlook Desktop do not support Modern Authentication for Outlook.com:  Outlook 2007, Outlook 2010, Outlook 2013, Outlook 2016 MSI, Outlook 2019 LTSC. Any release of Outlook Desktop with a version less than 11601.10000 does not support Modern Authentication for Outlook.com.

Outlook apps are available for free and can be downloaded directly from the Microsoft Store on Windows, the Mac App Store, iOS App Store, or the Google Play Store.  

After your download the new email app, add your accounts and they will all be configured to use Modern Authentication and sync properly, helping keep them safe.

So my version of Outlook that I installed will no longer support Basic Authentication? How do I know if it is an Outlook 2016 MSI version?

HI.