Forwarding gmail to xfinity email

I forward my gmail account to my Xfinity account to make it easier to keep track of (I don't have to log into two different sites to see my email).

I have just discovered that Xfinity is blocking the emails from gmail. I get an error message: see attachment. The link to additional details gives me several pages of suggestions, but nothing that seems immediately helpful.

I saw this question was raised several months ago but it was never resolved.