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popper(8)										popper(8)

       popper - pop 3 server

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

       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 speci-
       fications in RFC 1081 and RFC 1082.  The Berkeley server also has extensions to send elec-
       tronic mail on behalf of a client.

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

       The  POP  server  is  available	via anonymous ftp from ftp.CC.Berkeley.EDU (,	It is in two files in the pub  directory:  a  compressed  tar  file  pop-
       per.tar.Z and a Macintosh StuffIt archive in BinHex format called MacPOP.sit.hqx.

       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 instructions 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 cannonical 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 authen-
       tication fails, a warning message 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 /usr/spool/mail) which is used for all subsequent transactions.  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  (possi-
       bly) modified temporary maildrop.

       The  POP  server  uses syslog to keep a record of its activities.  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 priority "debug".  The default log file
       is /usr/spool/mqueue/POPlog.  These can be changed, if desired.	On systems with 4.2  sys-
       logging all messages are logged to the local log file, usually /usr/spool/mqueue/syslog.

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

       Extensive  re-write  of	the maildrop processing code contributed by Viktor Dukhovni <vik-
       tor@math.princeton.edu> that greatly reduces the possibility that the maildrop can be cor-
       rupted 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  tem-
       porary 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 spec-
       ifying  the  DEGUG  compiler  flag.   Note:   You still need to use the -d or -t option to
       obtain debugging output.

       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 exam-
       ple, 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 terminates.  This problem is being worked on and will be fixed in a
       later release.

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

       inetd(8), RFC1081, RFC1082

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

4.3 Berkeley Distribution		November 27, 1996				popper(8)
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