On my iPad I have 3 email accounts.
Never touched the settings but it now comes up and says the user name or pass word is wrong.
The non hotmail account is fine and its only emails out that don’t work on the hotmails.

Do you have the option where you change your password after set duration?
You could also try deleting account then reinstall it.

Mine does this constantly, on the iPad and my iPhone. Its a pain in the arrse, I haven’t been able to find any info on the net about sorting it out once and for all.

I did have to change password. If that was the problem surely it would stop mail coming in.

Think there is an option on full site to either keep same password or change after certain time scale.