popper(8) System Manager's Manual 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 Mac-
intosh 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 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(s).
HOW TO OBTAIN THE SERVER
The POP server is available via anonymous ftp from ftp.CC.Berkeley.EDU (126.96.36.199, 188.8.131.52). It is in two files in the pub direc-
tory: a compressed tar file popper.tar.Z and a Macintosh StuffIt archive in BinHex format 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 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 identi-
fied, 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 com-
mands 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.
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,
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.
VERSION 1.7 RELEASE NOTES
Extensive re-write of the maildrop processing code contributed by Viktor Dukhovni <email@example.com> that greatly reduces the pos-
sibility 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.
The POP server copies the user's entire maildrop to /tmp and then operates on that copy. If the maildrop is particularly large, or inade-
quate 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.
/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)