CheckUserAvailable()
From Rackspace Email & Apps API
This function will report whether a name exists as either an alias or as a mailbox on the domain.
Input Parameters
Four strings:
Administrative username, Administrative password, Domain name, Name to check
Return Values
If successful, the return value of the function will be 1 if the user name is available, -3 if already in use.
Consult the Result Code Table for a list of result codes and their meaning.
