Comcast email is POP3 unless, as rcobourn pointed out, you have transferred your email account through Comcast to imap. Email through POP3 does not support push delivery, on an iPhone or Android, it is polled on a fetch schedule and you set those parameters in the email app on the device. If you want to use the stock email app, make sure your email server settings are correct for Comcast. The incoming server should be set at mail.comcast.net port 995, the outgoing mail server should be set at smtp.comcast.net port 587, SSL should be on and authenticate with your Comcast ID and password. You can set the frequency of the fetch schedule to suit your needs.
I also use a Comcast account that I have had for a long while. I set my Comcast account to forward to my Gmail account. That way as soon as any email hits my Comcast account it is immediately forwarded to my Gmail and I get it instantly without having to wait on a fetch schedule or use a manual refresh. I have also set my Gmail account to allow the use of my Comcast email address as a reply from, so when I'm replying to email through my Gmail account I can choose my Gmail or Comcast email as the replying email address. This an alternative you may want to consider.