Check the message with Comcast's Xfinity Connect webmail and look for the Xfinity Verified Email logo next to any message that claims to be from Comcast/Xfinity (see https://www.xfinity.com/support/articles/comcast-verified-email).
XfinityPlease see Comcast Email Phish or Legit? How to Tell (and rules for posting) for more information about scam emails. The article is somewhat out of date, but still useful.
Samples of recent phishing messages can be found at http://constantguard.comcast.net/help/alerts under "Top Phishing Scams".