I should also add that you'd have problems on prime and illuminated since only x10premium would allow unlimited email accounts (who's ever heard of an email hosting service that only allows 3 or 6 clients at once?), and even on x10premium you'd have MAJOR problems combatting spam - we hold the account owner responsible for spam sent out from their account, and it's a fair bet -someone- will send spam sooner than never.
In addition, reading the x10premium TOS reveals that there is indeed a SPAM clause - if caught spamming you are immediately and permanently suspended. Unless you actually own the server itself (dedicated), I don't recommend trying to run an email hosting service - the penalties are too large to handle unless you actually control everything.