# 2.11BSD#431 - /usr/man/cat8/popper.0

    popper(8)	    UNIX Programmer's Manual		popper(8)

    NAME
         popper - pop 3 server

    SYNOPSIS
         /usr/libexec/popper [ -d ] [ -t trace-file]

    DESCRIPTION
         Popper is an implementation  of  the  Post  Office  Protocol
         server  that  runs  on a variety of Unix computers to manage
         electronic mail for Macintosh  and  MS-DOS  computers.   The
         server  was  developed  at  the  University of California at
         Berkeley and conforms fully to  the  specifications  in  RFC
         1081  and RFC 1082.  The Berkeley server also has extensions
         to send electronic mail on behalf of a client.

         The -d flag sets the socket to debugging and turns on debug-
         ging.   All  debugging information is saved using syslog(8).
         The -t trace-file flag turns  on  debugging  and  saves  the
         trace information in trace-file using fprintf(s).

    HOW TO OBTAIN THE SERVER
         The  POP  server  is  available  via  anonymous   ftp   from
         ftp.CC.Berkeley.EDU (128.32.136.9, 128.32.206.12).  It is in
         two files in  the	pub  directory:  a  compressed	tar  file
         popper.tar.Z  and a Macintosh StuffIt archive in BinHex for-
         mat called MacPOP.sit.hqx.

    THE POP TRANSACTION CYCLE
         The Berkeley POP server is a single program (called  popper)
         that  is launched by inetd when it gets a service request on
         the POP TCP port.	(The official port  number  specified  in
         RFC  1081 for POP version 3 is port 110.  However, some POP3
         clients attempt to contact the server at port 109,  the  POP
         version  2  port.	Unless you are running both POP2 and POP3
         servers, you can simply define both ports	for  use  by  the
         POP3 server.  This is explained in the installation instruc-
         tions later on.) The popper program initializes and verifies
         that  the peer IP address is registered in the local domain,
         logging a warning message when a connection  is  made  to	a
         client whose IP address does not have a canonical name.  For
         systems using BSD 4.3 bind, it also checks to see if a  can-
         nonical  name lookup for the client returns the same peer IP
         address, logging a warning message if it does not.  The  the
         server  enters  the  authorization  state,  during which the
         client must correctly identify itself by providing  a  valid
         Unix  userid  and password on the server's host machine.  No
         other exchanges are allowed during this state (other than	a
         request  to  quit.)  If authentication fails, a warning mes-
         sage is logged and the session ends.  Once the user is iden-
         tified,  popper changes its user and group ids to match that
         of the user and enters the transaction  state.   The  server
         makes a temporary copy of the user's maildrop (ordinarily in

    Printed 11/24/99	November 27, 1996			1

    popper(8)	    UNIX Programmer's Manual		popper(8)

         /usr/spool/mail) which is used for all  subsequent  transac-
         tions.   These  include the bulk of POP commands to retrieve
         mail, delete mail, undelete mail, and so forth.  A  Berkeley
         extension	also  allows  the user to submit a mail parcel to
         the server who mails it using  the  sendmail  program  (this
         extension	is  supported in the HyperMail client distributed
         with the server).	When the client quits, the server  enters
         the  final  update state during which the network connection
         is terminated and the user's maildrop is  updated	with  the
         (possibly) modified temporary maildrop.

    LOGGING
         The POP server uses syslog to keep a record of  its  activi-
         ties.   On  systems with BSD 4.3 syslogging, the server logs
         (by default) to the "local0" facility at  priority  "notice"
         for  all messages except debugging which is logged at prior-
         ity    "debug".	  The	  default     log     file     is
         /usr/spool/mqueue/POPlog.	These can be changed, if desired.
         On systems with 4.2 syslogging all messages  are  logged  to
         the local log file, usually /usr/spool/mqueue/syslog.

    DEBUGGING
         The popper program will log debugging information	when  the
         -d  parameter  is	specified  after  its  invocation  in the
         inetd.conf file.  Care should be  exercised  in  using  this
         option  since it generates considerable output in the syslog
         file.  Alternatively, the "-t <file-name>" option will place
         debugging	information into file "<file-name>" using fprintf
         instead of syslog.

         For SunOS version 3.5, the popper	program  is  launched  by
         inetd  from  /etc/servers.   This file does not allow you to
         specify command line arguments.  Therefore, if you  want  to
         enable   debugging,  you  can  specify  a	shell  script  in
         /etc/servers to be launched instead of popper  and  in  this
         script call popper with the desired arguments.

         You can confirm that the POP server is running  on  Unix  by
         telneting	to  port  110 (or 109 if you set it up that way).
         For example:

         %telnet myhost 110
         Trying...
         Connected to myhost.berkeley.edu.
         Escape character is '^]'.
         +OK UCB Pop server (version 1.6) at myhost starting.
         quit
         Connection closed by foreign host.

    VERSION 1.7 RELEASE NOTES
         Extensive re-write of the maildrop processing  code  contri-
         buted  by	Viktor	Dukhovni <viktor@math.princeton.edu> that

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    popper(8)	    UNIX Programmer's Manual		popper(8)

         greatly reduces the possibility that  the	maildrop  can  be
         corrupted	as  the  result  of simultaneous access by two or
         more processes.

         Added "pop_dropcopy" module to create a  temporary  maildrop
         from  the	existing,  standard  maildrop  as root before the
         setuid and setgid for the user is	done.	This  allows  the
         temporary	maildrop  to be created in a mail spool area that
         is not world read-writable.

         This version does *not* send the sendmail "From "	delimiter
         line in response to a TOP or RETR command.

         Encased all debugging code in #ifdef DEBUG constructs.  This
         code  can be included by specifying the DEGUG compiler flag.
         Note:  You still need to use the -d or -t option  to  obtain
         debugging output.

    LIMITATIONS
         The POP server copies the user's entire maildrop to /tmp and
         then operates on that copy.  If the maildrop is particularly
         large, or inadequate space is available in  /tmp,	then  the
         server will refuse to continue and terminate the connection.

         Simultaneous modification of a single maildrop can result in
         confusing	results.  For example, manipulating messages in a
         maildrop using the Unix /usr/ucb/mail command while  a  copy
         of  it  is  being	processed by the POP server can cause the
         changes made by one program to be lost when the  other  ter-
         minates.	This problem is being worked on and will be fixed
         in a later release.

    FILES
         /usr/spool/mail	     mail files
         /etc/inetd.conf	     pop program invocation
         /etc/syslog.conf	     logging specifications

    SEE ALSO
         inetd(8), RFC1081, RFC1082

    AUTHORS
         Bob Campbell, Edward Moy, Austin Shelton, Marshall  T  Rose,
         and cast of thousands at Rand, UDel, UCI, and elsewhere

    Printed 11/24/99	November 27, 1996			3

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