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Internet Exchange Frequently Asked Questions

Internet Exchange Messaging Server
POP3 Server FAQ

Introduction
The Internet Exchange Message Store (both Enterprise and Workgroup versions) provides a POP3 server so that remote clients may access their INBOX using the Post Office Protocol Version 3 (POP3) protocol.  Most email clients, such as Outlook Express, Eudora, Netscape Communicator, and many more support this standard.  Using POP3, users retrieve messages from the POP3 server and store them in a local hard disk so that they can be read in an off-line environment.   The Internet Exchange POP3 Server is a 32-bit application that supports multithreading for simultaneous processing of messages, thereby assuring fast message delivery.

Technical Overview
While the Internet Exchange POP3 Server is running, it listens on port 110 for a connection request from a POP3 client.  Once such a request is received, the POP3 Server creates a thread that will handle further client transactions.   Upon start-up, this server thread sends out an initial greeting to the client, signifying that a connection between the client and server has ben established.  After a connection has been established, the POP3 Server and its client communicate by a sequence of command response exchanges (see RFC-1081 for the POP3 command and response specifications), the goal of which is to retrieve all messages currently in the user's INBOX.  Specifically, the client sends POP3 commands to the server, which then executes the appropriate actions in response to these commands.  Based on the result of command execution, the server forms an appropriate response, which it sends back to the client.  If the POP3 Server encounters an error during execution, it sends back an error message to the user via the client screen.

In order to download messages, the user must first identify itself to the POP3 Server through his POP3 client account.  Thus, the initial commands that a POP3 client usually issues are the USER and PASS commands, which send the user name and password, respectively, to the POP3 Server for validation.  When the USER and PASS commands have been received, the server verifies the given user account information by checking for its existence in the Users Database.  Once the user name and password have been verified, the user's incoming mailbox is opened for the POP3 client's exclusinve use.  If another user, which may either be a POP3 client or an IMAP4 client, has already opened the incoming mailbox, access to that particular mailbox will not be allowed and the connection will be terminated.

Additional background information on POP3 can be found in the IMA Whitepaper Post Office Protocol Version 3 (POP3) and Internet Electronic Mail.

Incoming Mailbox as a Subdirectory of The MsgStore Directory
In the Message Store, the mailbox for incoming messages or INBOX is implemented as a subdirectory of the MsgStore directory containing message databases and actual message files.  Because mailbox and message status information is stored in relational databases, retrieval of this information is relatively fast.  Forthermore, because each message is assigned its own file, as opposed to a scheme wherein all messages are stored in a single file, message text is obtained without having to determine and seek for its position within a file.   Deletion of a message is likewise more straightforward as there is no need to move message text in order to overwrite the message that is to be deleted.

Auto-Logout Timer
The POP3 Server has an inactivity logout timer that causes the severance of a client connection once no command is received from the client within a period of 30 minutes, though this value is fully configurable.   The presence of this timer ensures that resources are not wasted on idle clients or on clients that have encountered problems and are not able to communicate with the server anymore.