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).
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 directory: a compressed tar file pop-
per.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 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.
VERSION 1.7 RELEASE NOTES
Extensive re-write of the maildrop processing code contributed by Viktor Dukhovni <vik-
email@example.com> 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
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
/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)