Resolution:
An ALE Message Handler acts as a bridge between SAP R/3 and other applications. It receives intermediate documents (IDOCs) from one or more instances of SAP R/3 and carries them to applications for processing. Likewise, it sends IDOCs received from applications to one or more SAP R/3 instances.
In contrast to an ALE converter, the message handler will not do any conversion or mapping but instead delivers IDOCs without changing them. It is assumed that a message handler has some sort of queuing mechanism and guarantees reliable delivery.