Mail app unable to receive Comcast email on certain Wi-Fi networks

On certain Wi-Fi networks I am unable to receive Comcast email using the Mail App. This occurs across devices: Laptop, iPhone, iPad. If I use the cellular connection on the iPad or iPhone, the emails come fine. If I log in to Comcast email on Safari while on these Wi-Fi networks, the mail loads normally on the browser page.

Other people have the same issue with these networks who are not on my Comcast account (but they do have Comcast accounts.) My Google email address works fine in the Mail App on these networks. On most Wi-Fi networks I don't have a problem at all, but on select ones, it's a real pain. Any thoughts?

Thanks.