From their site: Our Application Programming Interface (API) is platform independent and provides customers and resellers with the ability to securely integrate many facets of our administrative functions with third party software applications. Built upon the open standards of XML Web Services, customers can remotely "connect" to email management tools using a wide variety of SOAP enabled programming languages such as Java, ASP, Perl, and .NET.
Service providers are able to leverage the API to securely provision customer domains, mailboxes and related services in real-time using their own in-house systems. The API provides functions for grouping customer domains into sub-accounts and assigning delegated administration rights. This provides each sub-account with class-of-service controls for allotted storage space, number of mailboxes, spam filtering, and virus scanning settings.