POP Module

  • Post Office Protocol (POP3)
  • Configuring the POP module
  • Specifying Passwords
  • Special Features
  • The XTND XMIT Extension
  • The CommuniGate Pro POP implements E-mail message retrieval using the POP3 Internet protocol (STD0053,RFC1939, RFC1734, RFC1725) via TCP/IP networks.

    Post Office Protocol (POP3)

    The Post Office Protocol allows computers to retrieve messages from mailboxes on mail servers. A computer running a mailer (mail client) application connects to the mail server computer and provides account (user) name and the password. If access to the specified user account is granted, the mail application sends protocol commands to the mail server. These protocol commands tell the server to list all messages in the mailbox, to retrieve certain messages, or to delete them. When a server receives a request to retrieve a message, it sends the entire message to the mail client. The mail client may choose to retrieve only the first part of the message.

    The POP3 protocol does not support multi-mailbox accounts. If a client application specifies a multi-mailbox (folder) account, the INBOX mailbox is opened.

    When the client application sends a request to delete a message from the mailbox, the message is not deleted immediately, but it is marked by the server. Only when the client application ends the session properly and closes the connection, the marked messages are then removed.

    The POP module supports the XTND XMIT extension of the POP protocol. This extension allows users to submit messages via the POP protocol instead of the SMTP protocol.


    Configuring the POP module

    Use a Web browser to configure the POP module.

    Use the Log Level setting to specify what kind of information the POP module should put in the Server Log. Usually you should use the Major (message transfer reports) or Problems (message transfer and non-fatal errors) levels. But when you experience problems with the POP module, you may want to set the Log Level setting to Low-Level or All Info: in this case protocol-level or link-level details will be recorded in the System Log as well. When the problem is solved, set the Log Level setting to its regular value, otherwise your System Log files will grow in size very quickly.

    The POP module records in the System Log are marked with the POP tag.

    When you specify a non-zero value for the Maximum Number of Channels setting, the POP module creates a so-called "listener". The module starts to accept all POP connections that mail clients establish in order to retrieve mail from your server. The setting is used to limit the number of simultaneous connections the POP module can accept. If there are too many incoming connections open, the module will reject new connections, and the mail client should retry later.


    Specifying Passwords

    The POP module can use 2 passwords per account. See the Registering Users chapter for the details.


    Special Features

    Unlike many other POP servers, the CommuniGate Pro POP module does not "lock" the mailbox it opens on a mail clients behalf. This means that:

    Since the POP3 protocol was not designed to support these features, the CommuniGate Pro POP module:

    When a client mailer retrieves a message with the RETR command, the message is marked with the "Seen" flag (this change is noticed when using an IMAP client with the same mailbox). The TOP command that allows a client POP mailer to retrieve only the first part of the message does not set the Seen flag.


    The XTND XMIT Extension

    The CommuniGate Pro POP module implements the XTND XMIT protocol extension. Mailer applications that support this extension (like Eudora®) can submit messages to the Server via a POP connection.

    This feature can be useful for mobile users that would be otherwise unable to send their messages via CommuniGate Pro SMTP due to the Server anti-spam protection. Submitting messages via POP can be more convenient than using the "address-remembering" scheme, since this method does not have time restrictions.