I've written previously about ISP-provided email addresses and how risky they are. To recap, you're at the mercy of your ISP when you use an address such as firstname.lastname@example.org or email@example.com. Numerous people at broadbandreports.com have reported problems with their Comcast email. The only common factor seems to be that Comcast's system is too complex. Because your email address is tied to your account which is tied to every other service Comcast offers, people have found their emails locked due to anything from late payments to installation of phone service.
Previously, I mentioned another concern: Switch providers and you must leave your address behind. Few ISPs providers let you keep your address or offer to forward your email.
As if to prove me wrong, one of my friends found himself in this very situation when he switched from Comcast to Verizon a year ago. He had long been using a comcast.net address, had given it out to many people, and had subscribed to various mailing lists with it. And he figured the address would stop working when he left Comcast.
But the comcast.net address continued working. So he continued using it.
Curiously, Comcast didn't turn it off or ask for it back. Until...
About a year later, he decided he didn't like Verizon and wanted to go back to Comcast. Even I couldn't have guessed what would happen next: As soon as he opened a new account with Comcast, his old Comcast email address stopped working!
After calls to the local office proved unhelpful, he called Comcast's corporate headquarters in Philadelphia, each time being referred to an Executive Response Team member who would vow to fix the problem. After weeks of getting nowhere, he tracked down a technician who seemed to understand - but lacked the immediate access to make the needed changes. But enough badgering and finally someone got through and my friend got his email account back. It only took my friend hours of time on the phone spread over 60 days - for a fix that shouldn't have taken more than 10 minutes.
You may want to put that in the "just asking for trouble" category. After all, my friend did continue using a Comcast service (an email address) despite no longer being a customer. But I think you're at significant risk even if you are a Comcast customer in good standing. Case in point: A poster (userid: baffled) on dslreports.com described that an email address he had used for 4 1/2 years recently stopped working. When he called, Comcast told him that that another customer with the same name in Texas closed his Comcast account and the email address was "owned" by the Texan. (Clearly Comcast's idea of "ownership" is pretty weak if you can "own" it one day and "not own" it the next.) Anyway, since Mr. Texas was the "legal owner" of the email address, Comcast said there was nothing they could do.
In addition, baffled found that his sub-account email addresses were inoperative as well including one that he used as a business address. Fortunately, Comcast was able to resolve his problem in just 24 hours. It was just an accident! Our bad!
Ultimately, he got his accounts back along with his emails. But I would've bet against it. It is apparent from these and other stories that Comcast is not concerned with the way they handle email addresses.
If anyone can show me an ISP that provides any kind of guarantees on their mail service, I'd love to see it. Until then, I restate my earlier advice: Using ISP-provided email addresses is just too risky. And using them for business is insane.