Outlook 2016 doesn't accept password or app password

AnotherBug,

I understand what you are saying. In the case of Thunderbird, it offers POP and IMAP. That likely means that Thunderbird may not support EAS with OAuth. That means we are back to trying to get EAS with basic auth working and that is a degraded experience. Please ask the email client provider if they can support EAS with OAuth for Outlook.com. I found there is an EAS add-on for Thunderbird but it must use basic auth because users say it stopped working in late January, Provider for Exchange ActiveSync :: Reviews :: Add-ons for Thunderbird. If you or Rob have not tried this one it might be worth it and to give feedback so the developer will update for EAS with OAuth.

Thanks Gabriel, but please don't think I haven't tried that (and dozens of other "fixes" to undo the damage MS has imposed on its users for a month and counting).

However, my issue has never been with connectivity to email. I have been unable to maintain a stable connection to my calendar and contacts. The required plug-in is called TBSync. And though it provides an option to connect via OAuth2, it has rejected my Hotmail login credentials every time since January 23 -- throwing a variety of errors including (but not limited to):

Could not authenticate, check username and password (HTTP Error 401)

Could not connect to server (NS_ERROR_UNKNOWN_HOST)

Status.451

User not found (HTTP Error 404).

And when I do succeed in getting a connection using the Exchange setup option, it lasts only a few hours, sometimes a few days. To be clear, I have added and removed the account, and the plug in more than a few times. Nothing has produced a stable connection since all this began a month ago.

Thanks!

AnotherBug,

I do not have an Android phone to test the Gmail app to confirm the settings. I found the Gmail Mail App support article that has instructions for adding the account, Add another email account to the Gmail app - Android - Gmail Help (google.com). It's fairly limited steps but I would assume it uses OAuth for the connection.

I also found there is some Microsoft guidance for the Gmail app but I cannot easily test it to make sure its current or not affected by the basic auth limits, Set up email in Android email app - Microsoft Support.

Concerning the proxy also known as cloud cache there is nothing nefarious about it. If Microsoft abused customer data in any way it would have issues with regulators. Because of this it's actually easier to get into Fort Knox than to access customer data. No one at Microsoft can go look at your email data and no one has any interest in that. The only reason for cloud cache is to make it so Outlook is connecting to your third-party mailbox so that it appears as an Exchange account so that Outlook can provide you with all the features that come with it. This article explains what all cloud cache is for, Sync your account in Outlook to the Microsoft Cloud - Microsoft Support.

Microsoft have got this one badly wrong, many people have a very big problem with being forced to ingress all their third-party emails into Microsoft's systems just so they can use whatever new client you are peddling.

It won't matter, third-party clients will succeed where "new Outlook" falters, just look at the huge increase in donations Thunderbird is getting.