gmail-->xfinity forwarding -- not longer forwarding accurately

I know this had been raised in the past -- and never fully resolved! -- but I am having trouble forwarding my email from Gmail into my @comcast.net email address. Worked flawlessly for years but now I get messages blocked by the Comcast email server with various error codes ("throttling" and other anti-spam measures). How is Gmail not a trusted server? How can I fix this?? It's not every message but a mix of unimportant emails (like sales pitches from retailers) and very important emails (from friends and business contacts).