I would look for 'e-mail hosting' in google
Here is one company which may provide the service you need:
http://www.fusemail.com/
I don't know if they are flexible enough when it comes to billing of your own.
Everyone.net is also well-known for similar services.
Basically you don't have to provide a server, you just delegate the domain to their name servers.
As for the tax implications I cannot really advise. Are you a business owner or DBA ?
As for the legal implications properly written T&C are critical
