I can't add a secondary xfinity email account to the mail browser

I can access both my primary and secondary email accounts separately from the xfinity website.  I wish to add the secondary email account to the primary email account so I don't have to keep logging out and logging back in to each account.

Whenever I click the "add mail account" link in the navigation pane of the email browser i get "autoconfigure failed" so I try to configure it manually.  When I do that, I get "Validation of imap.comcast.net due to invalid credentials."  I tried all the recommended security settings without success.

I used to access my email through outlook, but that same secondary email stopped working there too, and I couldn't fix it there either.  Strange because my primary still works fine, and I can still access that secondary email just fine through the xfinity website.  I just can't access it anywhere else.