ModifyDomainMaxNumUsers()
From Rackspace Email & Apps API
This function will change the maximum number of mailboxes that can be created for a domain. Please note that mailbox and domain aliases do not count towards the total number of mailboxes. A limit of 0 is the same as saying that there are no limits to the number of mailboxes that may be created for the domain. Please use the "0" cautiously and be certain that your contract with us permits this to prevent billing problems.
Parameters
Three strings, one integer:
Administrative username, Administrative password, Domain name, Maximum mailbox count (integer, must be 0 or greater, 0 = no limit)
Return Values
If successful, the return value of the function will be 1.
Consult the Result Code Table for a list of result codes and their meaning.