IMAP

Apple mail is problematic.  I see this on my own mail servers.  The program tries to automatically configure the mail settings trying different protocols.  If you have several Xfinity accounts, or are checking mail on several Apple devices from the same IP address, to the server side it looks like an authentication bomb and it will toss you into authentication jail.  This is especially true if you change your password.  It's a misbehaving email client.

Log into webmail from a browser (xfinity.com).  Verify your username and password.  Now disable Xfinity email accounts on your phone and iPad. Stop anything else on your network checking your mail.  Wait 15-30 minutes, then try to enable ONE account on your phone.  If that works, wait for it to load mail before trying to enable the next account.

* Another real common one?  iPhone/iPad likes to capitalize the first letter in a dialogue box automatically.  It's a problem if your password doesn't have a capitol letter for the first character. You aren't entering the right password then. 

@user_bd84b2 Hello, thank you for reaching out to us on our Xfinity Community Forums. I'm bummed to hear you are having issues with outlook requests regarding password. Can you share any further details and update? We love to help figure things out. Let us know.