Outlook 2016 doesn't accept password or app password

As they say, the grass is always greener. I moved my email domain to Outlook after many problems with the G one. This is the first time in 10 years that there has been an issue, and at that it is only on my phone, my PCs using Outlook and modern auth have had 0 issues.

Outlook 2021 on W10 should not have any problems. Do you have 2FA enabled on your account and using modern auth (not a password or app password) in Outlook?

The mobile network vs wifi is a timing thing. Each time you connect, you get a random server at MS. Some are working fine, some are not. So if you toggle your wifi again, that time it might work fine on wifi, but not on mobile network.

They aren't blocking IPs so far as I can tell (except when you try too many times in a short period, it does seem to block it for a little while), it is just based on the server you get assigned by DNS randomly.

exactly. im with outlook 2019. password prompts were becoming less frequent in the last two days, I thought maybe MS was having it fixed. Boy, was I wrong! I started getting prompts couple times an hour today again!!!

The company I work for is using Office 365 for Business. I have a supplier/partner account with one of my customers that is on Google Workspace. The amount of issues on Office 365 is so alarming that I am talking to our IT about switching. Google's stuff just humming along with zero issue. So much so, I sometimes send myself a test email to see if the account connection is still alive - and it is.

With Office 365, if it's not password prompt, it's that stupid 2FA/MFA prompt that has a "...don't ask again for 365 days..." box. Even checked, I get the prompt at random well before 365-days is reached, even before this current issue. These are critical accounts, so I have very secured randomly generated passwords and I don't have the password manager on my phone, so every time I get 2FA challenged out of normal, I can't address it until I am back near my computer. If it's not password issue, it's sync issue. My calendar and contacts are not auto-sync'ed, even though the setting is set to auto-sync. Again, no issue on Google. The moment I add a calendar or contact, it's on my phone within a few seconds. With Office 365 and working EAS connection, I have to manually go to the account setting and force it to sync to get updates.

I travel constantly for work and Google challenges me the same way I expect it should - when I go to far and random places that I never go to. With Microsoft, it's so stupid that it's beyond words - always challenge me at my foreign office, or the same hotel I've stayed at for years, both of which has fixed IP addresses. When I go to some random places where I think it highly risky, MS doesn't challenge me.

If you also look at spams, vast vast majority of them are transmitted on Microsoft infrastructure from Russia and East European spammers. Microsoft seems to have no way to stop them effectively. Ironically, I have gotten a lot less Microsoft-originated spams on my non-MS accounts from since this current issue. At least there is one little benefit out of this whole mess - spammers probably have a harder time to send spams.