popa3d man page on Slackware

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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 pass‐
       word 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 dae‐
	      mon, accepting connections on the pop3 port (110/tcp) and	 fork‐
	      ing  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  sig‐
	      nificantly 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-insen‐
       sitive).

       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)
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