2.11BSD/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
_P_o_p_p_e_r 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 _t_r_a_c_e-_f_i_l_e 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
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/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
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