Can't retrieve comcast email on xfinity

I am having trouble receiving Comcast email in Outlook. I have 3 Comcast email addresses - the main account address and 2 additional email addresses. I successfully added 1 Comcast email to my Xfinity account and can now view emails for 2 addresses through my Xfinity account - the main account and the one just added. However, the 3rd email address - the one I am having trouble with in Outlook - will not set up in my Xfinity account. The error message in my Xfinity account says:

The entered credential or authentication information does not work or are no longer accepted by provider. Please change them.

Please advise.