Methods, systems, and computer program products that provide for a runtime messaging infrastructure, which abstracts send and receive operations for exchanging messages with partner endpoint. The messaging infrastructure improves availability and scalability of a message application by improving on the availability and scalability of the underlying message transports. In particular, availability and scalability are improved by linking the message application at runtime with any number of the message transports, without the message application specifying a transport at development time. The message infrastructure receives instructions from the message application specifying end-to-end delivery assurances. The infrastructure uses transports in order to fulfill the specified delivery assurance, and creates a link between the message application and transports for use in exchanging messages. Session state storage can be maintained in a pluggable store, which could be, for example, a durable database store or an application memory store.