I would really careful, they disappeared for months and our installation was hacked and spammers almost put us out of business. It was the worst event I have ever been through on the internet. One that I still am trying to repair with ISP's that get our email.
When offering free email or paid email accounts the lessons I learned were:
1 - Use another domain and another IP just in case spammers hack the site
2. - Only use professional systems that cost a fotune