1. A method for routing messages from one or more sending services to one or more recipient services across a message interchange network, said message interchange network being built on an open platform overlaying a public network and providing for application integration as a service, wherein at least some of the one or more sending services and the one or more recipient services are managed by different organizational entities, and wherein each sending service and recipient service is accessible according to properties and permissions associated with each of the sending services and recipient services, comprising: (a) receiving a message from a sending service, said message including a header element and at least one of: a body element including one or more documents that a sending service is sending to a recipient service, and an attachment including one or more documents that a sending service is sending to a recipient service; (b) determining a route path for delivery of said message to said one or more recipient services, said route path including one or more in-transit services, said determining being based on an evaluation of two or more routing scripts selected from the group consisting of: a routing script defined by a sending service, a routing script defined by a recipient service, and one or more routing scripts defined by one or more in-transit services, such that each service is capable of independently affecting said determining of said route path during a logical routing of said message represented by said evaluation; and (c) delivering said message to an in-transit service in said route path, wherein said in-transit service performs an identifiable operation on said message as said message travels from a sending service to a recipient service, the identifiable operation altering the content of the message to ensure that the message has the proper format for the recipient service.