This provides basic protection against message loss, but does not guarantee delivery under all circumstances.
When a connection aborts, TCP cannot reliably detect whether the last messages sent have actually reached their destination.
[1] Unlike the syslog protocol, RELP works with a backchannel which conveys information back to the sender about messages processed by the receiver.
During initial connection, sender and receiver negotiate session options, like supported command set or application level window size.
However, practical deployments use wrappers around the RELP session in order to provide that functionality.