DragonFly On-Line Manual Pages

POPA3D(8)                    System Administration                   POPA3D(8)

NAME
       popa3d - Post Office Protocol (POP3) server

SYNOPSIS
       popa3d [-D] [-V]

DESCRIPTION
       popa3d is a Post Office Protocol version 3 (POP3) server.

       A POP3 server operates on local mailboxes on behalf of its remote
       users.  Users can connect at any time to check their mailbox and fetch
       the mail that has accumulated.  The advantage of this "pull" approach
       is that any user with a simple POP3-capable mail reader program can
       receive mail, eschewing the need for a full-fledged Mail Transfer Agent
       (MTA) and a permanent network connection.

       Note that POP3 can only be used to retrieve mail, not to send it.  To
       send mail, the SMTP protocol is commonly used.

       For access to a mailbox through POP3, the username must be in the
       password database.  Additionally, popa3d does not permit null passwords
       and will refuse to serve mail for root (UID 0) users.

OPTIONS
       -D     Standalone server mode.  In this mode, popa3d will become a
              daemon, accepting connections on the pop3 port (110/tcp) and
              forking child processes to handle them.  This has lower overhead
              than starting popa3d from an inetd equivalent (which popa3d
              assumes by default) and is thus useful on busy servers to reduce
              load.  In this mode popa3d also does quite a few checks to
              significantly reduce the impact of connection flood attacks.

       -V     Print version information and exit.

COMMANDS
       A normal POP3 session progresses through three states: AUTHORIZATION,
       TRANSACTION, and UPDATE.

       After the TCP connection opens, the client must authenticate itself to
       the server during the AUTHORIZATION state.  The following commands are
       supported in the AUTHORIZATION state (all command names are case-
       insensitive).

       USER name
              Authenticate as user name.

       PASS string
              Authenticate using password string.

       QUIT   Quit; do not enter UPDATE state.

       When authorization is successful, the server enters the TRANSACTION
       state.  The client can now list and retrieve messages or mark messages
       for deletion.  The following commands are supported in the TRANSACTION
       state.

       DELE msg
              Mark message for deletion.

       LAST   Show highest message number accessed (obsolete).

       LIST [msg]
              List message number and size.

       NOOP   Do nothing.

       QUIT   Quit; enter UPDATE state.

       RETR msg
              Retrieve message.

       RSET   Clear deletion marks.

       STAT   Return total number of messages and total size.

       TOP msg n
              Show top n lines of message body.

       UIDL [msg]
              List message number and digest.

       When the client issues the QUIT command in the TRANSACTION state, the
       server enters the UPDATE state.  All messages that were marked for
       deletion are now removed.  The server then closes the connection.

BUGS
       POP3 transmits passwords in plaintext and thus, if you care about the
       security of your individual user accounts, should only be used either
       in trusted networks or tunneled over encrypted channels.

       There exist extensions to the protocol that are supposed to fix this
       problem.  popa3d does not support them yet, partly because this isn't
       going to fully fix the problem.  In fact, APOP and the weaker defined
       SASL mechanisms such as CRAM-MD5 may potentially be even less secure
       than transmission of plaintext passwords because of the requirement
       that plaintext equivalents be stored on the server.

AUTHORS
       Solar Designer <solar at openwall.com>

       This manual page is based heavily on the one Camiel Dobbelaar wrote for
       OpenBSD.

SEE ALSO
       Official Internet Protocol Standard STD 53, also known as RFC 1939.

       http://www.openwall.com/popa3d/

Openwall Project                 2 March 2003                        POPA3D(8)