I received a messge that I had to update my mail box to receive further messages. Is this true? I have not opened it.
Can't be sure without more information, but it sounds like a phishing email, a scammer attempt to steal login and account information. If you check your email with Comcast's Xfinity Connect webmail, 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).
Please see Comcast Email Phish or Legit? How to Tell (and rules for posting) for more information about identifying, reporting, and posting phishing 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 The article is somewhat out of date, but still useful.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".