1.3.4 Controlling Sending and Delivery of Mail

If a client is connected to several e-mail servers at once (not necessarily using the same protocol), it can choose to control how mail is sent by manipulating the spooler queue of the message store. If a client delivers mail into a folder on the server (such as delivering Post Office Protocol - Version 3 (POP3) messages), it can inform the server of the new mail through remote operation (ROP) requests.