Methods and systems for reliably exchanging a message among collaborating applications are disclosed. The methods and systems utilize a central exchange infrastructure (XI) for executing collaborative business processes among heterogeneous applications. Reliable message transmission is guaranteed by an Exactly Once Protocol (EOP), in which a database associated with the messaging and transport layer (MTL) of an HTTP-compliant server is used for storing a message identifier and comparing the message identifier to previously received message identifiers. If there is no match, the XI facilitates an exchange of message content of application data from a sending application to a receiving application.