You need to identify how you're trying to access your email, what app/client/browser/device and from what zip code. It could be a regional server access issue if not a local internet issue.
I'm not successful either. The app works. But not my browser. Chrome.
I've tried my saved link:https://xfinityconnect.mail.comcast.net
I've tried going from https://my.xfinity.com/?cid=cust and clicking the email icon.
While I was answering, I found I can access it using firefox. I had to get some pin code from comcast to access it.
Try a different browser, or clear your cache and cookies on the browser you like and try again.