popper(8)

NAME
popper - pop 3 server

SYNOPSIS
/usr/local/libexec/popper [ -d ] [ -s ] [ -k ] [ -t trace-file] [ -T timeout] [ -b bulldir]

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 1939.

The -d flag sets the socket to debugging and turns on debugging. 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(3V).

The -k flag enables kerberos authentication when popper has been compiled with the KERBEROS define. You must already have libraries that support Kerberos.

The -s flag turns on statistics logging using syslog(8). At the end of each popper session, the following information is logged: username, number of messages deleted, number of bytes deleted, number of message left on server, number of bytes left on server.

The -T timeout option changes the default compiled value POP_TIMEOUT for terminating a session with a pop client. When the server is waiting for a command to arrive from the client, it times out after the specified number of seconds and terminates the session. This avoids having popper processes hang forever waiting for command input from clients which have terminated abnormally. A small value is ok for small to medium nets where the network delay is within a few seconds. In this case 15-30 seconds is not unreasonable. Networks with large delays in sending packets (e.g., SLIP links) may require a larger value. In this case 300 seconds (5 minutes) is not unreasonable.

The -b bulldir option turns on the bulletin feature and specifies the bulletin directory path.

BULLETINS

The bulletin feature gives system administrators a way to send important announcements to all POP users without having to do mass mailings.

The bulletin directory contains one file per bulletin. Each file contains a single mail message with header and body in mailbox format. The first line of each such bulletin must be a "From " line. The easiest way for sysadmins to create such bulletins is to mail themselves a copy of the bulletin using the account to which they want replies to be sent, then use their mail program to save the message to a file in the bulletin directory in mailbox format. The bulletin directory must be world readable.

The name of each bulletin file begins with the bulletin number, and may optionally continue with any other characters. E.g., the file name of bulletin number 23 might be "23.pophost_down_sunday".

Popper creates a file named .popbull in the home directory of each user. This file contains a single line recording the highest numbered bulletin received by the user.

Each time a POP client connects to the server, any new bulletins which the user has not received previously are automatically appended to the user's mail.

When a bulletin is copied, the "To" header line is replaced by "To: username@thishost", and any "Status:" header lines are deleted. Otherwise, the bulletin is copied as is.

When a new user checks for mail the first time, popper creates the .popbull file in the user's home directory and seeds it with the current maximum bulletin number. Thus new users do not get old bulletins.

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 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 authentication fails, a warning message is logged and the session ends. Once the user is identified, 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 which is used for all subsequent transactions. These include the bulk of POP commands to retrieve mail, delete mail, undelete mail, and so forth. 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 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 /var/log/messages. 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.

EXTENSIONS

The server implements two extended commands.

XTND XMIT: Sends a mail message using /usr/sbin/sendmail.

XTND XLIST header [num]: Extracts and returns the specified header line for the specified message number. If the "num" parameter is missing, returns the header line for all the messages which are not currently marked for deletion.

FILES
/var/mail         mail files
/etc/inetd.conf         pop program invocation
/etc/syslog.conf        logging specifications
~/.popbull              largest bulletin number seen by user

SEE ALSO
inetd(8), RFC1081, RFC1082, RFC1939

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