@(#)@(#)README 2.6 2.6 4/2/91
The Post Office Protocol Server: Installation Guide
Introduction
The Post Office Protocol server runs on a variety of Unix[1] 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[2] and RFC 1082[3].
The Berkeley server also has extensions to send electronic mail on
behalf of a client.
This guide explains how to install the POP server on your Unix
computer. It assumes that you are not only familiar with Unix but also
capable of performing Unix system administration.
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-version.tar.Z and a Macintosh StuffIt archive
in BinHex format called MacPOP.sit.hqx.
Contents of the Distribution
The distribution contains the following:
+ All of the C source necessary to create the server program.
+ A visual representation of how the POP system works.
+ Reprints of RFC 1081 and RFC 1082.
+ A HyperCard stack POP client implementation using MacTCP.
+ A man page for the popper daemon.
+ This guide.
Compatibility
The Berkeley POP server has been successfully tested on the following
Unix operating systems:
+ Berkeley Systems Distribution 4.3
+ Sun Microsystems Operating System versions 3.5 and 4.0
+ Ultrix version 2.3
The following POP clients operate correctly with the Berkeley POP server:
+ The Berkeley HyperMail HyperCard stack for the Apple Macintosh
(distributed with the server).
+ The Stanford University Macintosh Internet Protocol MacMH program.
+ The Stanford University Personal Computer Internet Protocol MH
program.
+ The mh version 6.0 programs for Unix.
Support
The Berkeley POP server is not officially supported and is without any
warranty, explicit or implied. However, we are interested in your
experiences using the server. Bugs, comments and suggestions should be
sent electronically to netinfo@garnet.Berkeley.EDU.
Operational Characteristics
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 (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 (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
/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.
Problems
If the filesystem which holds the /usr/spool/mail fills up users will
experience difficulties. The filesystem must have enough space to hold
(approximately) two copies of the largest mail box. Popper (v1.81 and
above) is designed to be robust in the face of this problem, but you may
end up with a situation where some of the user's mail is in
/usr/spool/mail/.userid.pop
and some of the mail is in
/usr/spool/mail/userid
If this happens the System Administrator should clear enough disk space
so that the filesystem has at least as much free disk as both mailboxes
hold and probably a little more. Then the user should initiate a POP
session, and do nothing but quit. If the POP session ends without an
error the user can then use POP or another mail program to clean up his/her
mailbox.
Alternatively, the System Administrator can combine the two files (but
popper will do this for you if there is enough disk space).
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. (To enable debugging, you must edit the Makefile
to add -DDEBUG to the compiler options.)
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.
Installation
1. Examine this file for the latest information, warnings, etc.
2. Check the Makefile for conformity with your system.
3. Issue the make command in the directory containing the popper
source.
4. Issue the make install command in the directory containing the
popper source to copy the program to /usr/etc.
5. Enable syslogging:
+ For systems with 4.3 syslogging:
Add the following line to the /etc/syslog.conf file:
local0.notice;local0.debug /usr/spool/mqueue/POPlog
Create the empty file /usr/spool/mqueue/POPlog.
Kill and restart the syslogd daemon.
+ For systems with 4.2 syslogging:
Be sure that you are logging messages of priority 7 and higher.
For example:
7/usr/spool/mqueue/syslog
9/dev/null
6. Update /etc/services:
Add the following line to the /etc/services file:
pop 110/tcp
Note: This is the official port number for version 3 of the
Post Office Protocol as defined in RFC 1081. However, some
POP3 clients use port 109, the port number for the previous
version (2) of POP. Therefore you may also want to add the
following line to the /etc/services file:
pop2 109/tcp
For Sun systems running yp, also do the following:
+ Change to the /var/yp directory.
+ Issue the make services command.
7. Update the inetd daemon configuration. Include the second line ONLY if you
are running the server at both ports.
+ On BSD 4.3 and SunOS 4.0 systems, add the following line to the
/etc/inetd.conf file:
pop stream tcp nowait root /usr/etc/popper popper
pop2 stream tcp nowait root /usr/etc/popper popper
+ On Ultrix systems, add the following line to the
/etc/inetd.conf file:
pop stream tcp nowait /usr/etc/popper popper
pop2 stream tcp nowait /usr/etc/popper popper
+ On SunOS 3.5 systems, add the following line to the
/etc/servers file:
pop tcp /usr/etc/popper
pop2 tcp /usr/etc/popper
Kill and restart the inetd daemon.
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.
Release Notes
1.83 Make sure that everything we do as root is non-destructive.
1.82 Make the /usr/spool/mail/.userid.pop file owned by the user rather
than owned by root.
1.81 There were two versions of 1.7 floating around, 1.7b4 and 1.7b5.
The difference is that 1.7b5 attempted to save disk space on
/usr/spool/mail by deleting the users permanent maildrop after
making the temporary copy. Unfortunately, if compiled with
-DDEBUG, this version could easily wipe out a users' mail file.
This is now fixed.
This version also fixes a security hole for systems that have
/usr/spool/mail writeable by all users.
With this version we go to all new SCCS IDs for all files. This
is unfortunate, and we hope it is not too much of a problem.
Thanks to Steve Dorner of UIUC for pointing out the major problem.
1.7 Extensive re-write of the maildrop processing code contributed by
Viktor Dukhovni <viktor@math.princeton.edu> that 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.
1.6 Corrects a bug that causes the server to crash on SunOS
4.0 systems.
Uses varargs and vsprintf (if available) in pop_log and
pop_msg. This is enabled by the "HAVE_VSPRINTF"
compiler flag.
For systems with BSD 4.3 bind, performs a cannonical
name lookup and searches the returned address(es) for
the client's address, logging a warning message if it
is not located. This is enabled by the "BIND43"
comiler flag.
Removed all the includes from popper.h and distributed
them throughout the porgrams files, as needed.
Reformatted the source to convert tabs to spaces and
shorten lines for display on 80-column terminals.
1.5 Creates the temporary maildrop with mode "600" and
immediately unlinks it.
Uses client's IP address in lieu of a canonical name if
the latter cannot be obtained.
Added "-t <file-name>" option. The presence of this
option causes debugging output to be placed in the file
"file-name" using fprintf instead of the system log
file using syslog.
Corrected maildrop parsing problem.
1.4 Copies user's mail into a temporary maildrop on which
all subsequent activity is performed.
Added "pop_log" function and replaced "syslog" calls
throughout the code with it.
1.3 Corrected updating of Status: header line.
Added strncasecmp for systems that do not have one.
Used strncasecmp in all appropriate places. This is
enabled by the STRNCASECMP compiler flag.
1.2 Support for version 4.2 syslogging added. This is
enabled by the SYSLOG42 compiler flag.
1.1 Several bugs fixed.
1.0 Original version.
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 terminates. This
problem is being worked on and will be fixed in a later
release.
Credits
The POP server was written by Edward Moy and Austin Shelton with
contributions from Robert Campbell (U.C. Berkeley) and Viktor Dukhovni
(Princeton University). Edward Moy wrote the HyperMail stack and drew
the POP operation diagram. This installation guide was written by
Austin Shelton.
Footnotes
[1] Copyright (c) 1990 Regents of the University of California.
All rights reserved. The Berkeley software License Agreement
specifies the terms and conditions for redistribution. Unix is
a registered trademark of AT&T corporation. HyperCard and
Macintosh are registered trademarks of Apple Corporation.
[2] M. Rose, Post Office Protocol - Version 3. RFC 1081, NIC,
November 1988.
[3] M. Rose, Post Office Protocol - Version 3 Extended Service
Offerings. RFC 1082, NIC, November 1988.