XCLN: POP3 Requires QUIT Command Before Delete (141343)

SUMMARY

You may receive duplicate messages when retrieving Internet mail on subsequent connections with the Exchange Internet Provider, if your connection to the mail server is disrupted.

The Microsoft Exchange e-mail client, with the Exchange Internet Provider, transports messages through the Internet using Post Office Protocol Version 3 (POP3). This protocol requires that the client issue a QUIT command before the mail server removes messages marked for deletion.

If the connection is disrupted before the client can issue the QUIT command, all messages marked for deletion will remain on the server and be downloaded again on the next connection.

MORE INFORMATION

The Microsoft Exchange Internet Provider uses the POP3 protocol as outlined in RFC 1725. This is a protocol that outlines how e-mail clients connect to a POP3 server to send, retrieve, and delete mail.

When the client downloads mail from the POP3 server, it marks the messages for deletion unless COPY is specified from the Remote Mail menu in Exchange. After all messages are downloaded successfully, the Exchange client issues the POP3 command QUIT, which causes the session to enter the Update state. During the Update state, mail marked for deletion is removed from the server and the network session (TCP) is closed.

If a session terminates for some reason other than a client-issued QUIT command, the POP3 session does NOT enter the Update state and will not remove any messages from the server. This method assures that all messages are received OK before being deleted.

The QUIT command must be supported by all POP3 implemented servers and clients, including Microsoft Exchange.

Common problems that will cause an interrupted POP3 session include:

Lost carrier over a Dial-Up Networking connection via modem.
Failure at the network layer that causes TCP/IP connection to be dropped.
Call waiting signal on telephone line that causes a modem connection to be lost.
Down POP3 server.