The Email channel (Delphi only) implements asynchronous communication by using standard email and existing POP3 and SMTP servers to send requests to a server and retrieve responses.
The client channel is configured with the server's email address and uses that address to send requests off to the server for processing. The server will retrieve these emails from a POP3 mailbox, process the requests and eventually send the results back to the client, again via email. The client channel can poll its own POP3 mailbox to obtain the response.
This channel is ideal for running requests with long execution times that could potentially outlive a single client session. Since requests and responses are persisted in POP3 email boxes, a client application could send a request, exit, and then retrieve the response hours or even days later. Similarly, requests can be sent to a server that might not currently be running - when the server starts up it will catch up and process emails that are waiting in its email inbox.