Reference: Comcast Email Domains

[ comcast ]

Hey! I know that people find the ISP domain guides useful, so I thought I'd fire up the blog machine to share info about our friends at American telecommunications company Comcast (Xfinity) and their various email domains. I'm not sure that everybody knows this information already, so I though it would be good to share.

It's mostly pretty simple, and it boils down to this:

  • comcast.net: People who have cable internet service from Comcast (aka Xfinity) and who use Comcast's email service are going to have their mailboxes in this domain name.
  • comcast.com: Comcast employees are going to have their mailboxes in this domain.
  • cable.comcast.com: Comcast employees will be found here, too.
  • xfinity.com: does have an MX record and you might think it's alive for email, but I'm not seeing any widespread evidence that any significant number of mailboxes are hosted here.

If you run some sort of website where people signup for email messages from you, and if that website is mostly B2C (consumer) focused, your legitimate subscription attempts are going to come from comcast.NET. You're going to have a lot of people submit comcast.COM email addresses as well, and it's an open question as to how valid these are. Some of them could indeed be Comcast employees -- but a lot of them will be comcast.NET subscribers who confused .com and .net when providing their email address. Best to verify and validate, if you don't want to cause yourself deliverability issues.

To recap:

  • comcast.net: A legit domain for B2C subscriber signups.
  • comcast.com: A legit domain for B2B subscription requests from Comcast employees. NOT legit for B2C subscription requests from Comcast Xfinity customers.
  • cable.comcast.com: A legit domain for B2B subscription requests from Comcast employees. NOT legit for B2C subscription requests from Comcast Xfinity customers.
  • xfinity.com: Nobody home here, as far as I can tell.

There may be additional subdomains under comcast.com that are legitimate in that they have MX records and may accept mail, but they're probably servers mean to handle various bits of programmatically-sent email notifications, and they aren't likely to host lots of mailboxes that your typical email marketer is going to be sending mail to.

And finally, be sure not to cache the MX records for any Comcast domains (or really, any domains) beyond what the domain owner publishes in their TTL record. Comcast has indicated that they are in the process of moving to new inbound mail servers with new MX records for their domains. If you cache the old MX records for too long, you'll end up trying to connect to old mail servers that may or may not still be in service. Unpredictable things could happen, and successful email delivery will not be guaranteed.

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