I've got a friend who has his email set up with a custom domain, registered through Earthlink. He wants to change domain registrars. Earthlink simply hosts the domain and MX records which point to servers owned by "carrierzone". I've found some Google results that suggest carrierzone is connected with Earthlink. And carrierzone's website seems to say they're primarily some kind of spam filtering service. My friend hasn't heard of carrierzone before. I'm assuming they provide email hosting / SMTP service.
I'm hoping that I can help him switch registrars and simply copy the MX records to the new DNS servers, then cancel the Earthlink account. If my assumption that carrierzone provides email hosting and is not connected to the Earthlink account is correct, then this shouldn't interrupt his email service. Is this a valid assumption? Does anyone have any experience directly with carrierzone?