The Reliable Messaging feature defines an interoperable protocol for the MSHs to reliably exchange messages. That is, when an MSH sends a message, the recipient MSH receives the message once and only once. Reliable Messaging also handles the delivery and acknowledgment of ebXML Messages. The feature includes message handling for persistence, retry, error notification, duplicate detection, and acknowledgment of messages that require reliable messaging. Reliable Messaging is achieved when a receiver MSH responds to a message with an acknowledgment.