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popclient(1L) popclient(1L)
NAME
popclient - retrieve mail from a mailserver using Post
Office Protocol.
SYNOPSIS
popclient [-2 | -3] [-Vksv] [-u server-userid] [-p server-
password]
[-f remote-folder] [-c | -o local-folder] host
DESCRIPTION
popclient is a Post Office Protocol compliant mail
retrieval client which supports both POP2 (as specified in
RFC 937) and POP3 (RFC 1225).
Typically, popclient will be used to download mail in
batch from the remote mailserver specified by host to a
mail folder on the local disk. The retrieved mail will
then be manipulated using a local mail reader, such as
mail or elm.
To facilitate the use of popclient in scripts, pipelines,
etc, it returns an appropriate exit code upon termination
-- see EXIT CODES below.
OPTIONS
-2 Use Post Office Protocol version 2 (POP2).
-3 Use Post Office Protocol version 3 (POP3).
-k Keep messages in folder on remote mailserver. Nor-
mally, messages are deleted from the folder on the
mailserver after they have been retrieved. Speci-
fying -k causes retrieved messages to remain in
your folder on the mailserver.
-s Silent mode. Suppresses all progress/status mes-
sages that are normally echoed to stderr during a
POP connection. If both the -s and -v options are
specified, the -v option takes precedence.
-v Verbose mode. All control messages passed between
popclient and the mailserver are echoed to stderr.
Specifying -v causes normal progress/status mes-
sages which would be redundant or meaningless to be
modified or omitted.
-u Specifies the user idenfication to be used when
logging-in to the mailserver. The appropriate user
identification is both server and user dependent.
Default is your login name on the machine that is
running popclient. See USER AUTHENTICATION below
for a complete description.
-p Specifies the password to be used when logging-in
to the mailserver. The appropriate password is
both server and user dependent. If the -p option
is not used to specify a password, you will be
prompted for a password before the connection to
the mailserver is established. See USER AUTHENTI-
CATION below for a complete description.
-f Causes an alternate mail folder on the mailserver
to be retrieved. The syntax of the folder name is
server dependent, as is the default behavior when
no folder is specified. Fortunately, most POP
servers have a reasonable default behavior, so use
of this option should be limited to fairly special-
ized applications. POP3 does not provide a folder
specification in the protocol. If the -f option is
used in conjunction with the -3 option, the remote
folder specification is ignored.
-o Causes retrieved messages to be appended to an
alternate mail folder on the local disk. When nei-
ther -o nor -c is specified, retrieved messages are
appended to the system default mail folder. See
OUTPUT OPTIONS below for a complete description.
-c Causes retrieved messages to be written to stdout
instead of a mail folder. See OUTPUT OPTIONS below
for a complete description. You may not specify
both the -c and -o options on the same command
line.
-V Displays the version information for your copy of
popclient. If you specify the -V option, all other
options are ignored and no POP connection is made.
PROTOCOL SELECTION
The selection of the correct Post Office Protocol (POP2 or
POP3) depends upon the configuration of the mailserver
from which you retrieve your mail. The system adminstra-
tor who installed popclient on your system should have
chosen an appropriate default protocol for your
mailserver. If you get the message 'Connection refused'
when using the default protocol, try specifying -2 or -3
to select a different protocol. If the 'Connection
refused' message persists regardless of the protocol
selected, it is likely that your mailserver is not running
a POP compliant mail service.
USER AUTHENTICATION
User authentication in popclient is very much like the
authentication mechanism of ftp(1). The correct user-id
and password depend upon the underlying security system at
the mailserver.
If the mailserver is a Unix machine on which you have an
ordinary user account, your regular login name and pass-
word are used with popclient. If you use the same login
name on both the server and the client machines, you
needn't worry about specifying a user-id with the -u
option -- the default behavior will use your login name on
the client machine as the user-id on the server machine.
If you use a different login name on the server machine,
specify that login name with the -u option. e.g. if your
login name is 'jsmith' on a machine named 'mailgrunt', you
would start popclient as follows:
popclient -u jsmith mailgrunt
The default behavior of popclient is to prompt you for
your mailserver password before the POP connection is
established. This is the safest way to use popclient and
ensures that your password will not be compromised. You
may also specify your password using the -p option. This
is convenient when using popclient with automated scripts,
but it may result in your password being exposed to prying
eyes -- be careful! Regardless of how your password is
specified it is never stored in shared memory segments, or
left unencrypted in the core image when popclient termi-
nates. Continuing the preceding example, suppose your
password on 'mailgrunt' is 'Gr8PassWd'. The syntax would
be:
popclient -u jsmith -p Gr8PassWd mailgrunt
On mailservers that do not provide ordinary user accounts,
your user-id and password are usually assigned by the
server administrator when you apply for a mailbox on the
server. Contact your server administrator if you don't
know the correct user-id and password for your mailbox
account.
OUTPUT OPTIONS
popclient always writes the retrieved messages using Unix
mail folder format. This allows popclient to be used in
conjunction with common mail readers like mail and elm.
The retrieved messages are normally appended to your
default system mailbox on the local disk, using the local
Mail Delivery Agent (MDA), usually /bin/mail(1), so that
when you invoke your mail reader it can manipulate the
retrieved messages like any other mail you receive on the
client machine.
Using the -o option, you can specify a different mail
folder to which the retrieved messages will be appended.
If you prefer, for example, to have your POP mail from a
machine called 'mailgrunt' stored in the mbox file in your
home directory, you would start popclient as follows:
popclient -o $HOME/mbox mailgrunt
Note that the folder specified with -o is not locked or
otherwise protected from other processes writing to it
while popclient is writing to it.
popclient can be used in a shell pipeline by using the -c
option. In this mode, popclient writes the retrieved mes-
sages to stdout, instead of a mail folder. This would
allow you, for instance, to pass the incoming mail through
a filter that discards mail marked as 'Precedence: junk'.
Suppose you've written an AWK script called 'dumpjunk.awk'
to implement a junk mail filter. The appropriate syntax
to retrieve your mail from 'mailgrunt', pass it through
the filter, and write it to a folder called 'realmail' in
your home directory would be:
popclient -c mailgrunt | awk -f dumpjunk.awk >
$HOME/realmail
The progress/status messages written to stderr when the -s
option has not been specified, do not interfere with the
message stream, which is written to stdout. You may even
use -v and -c together without corrupting the message
stream. It is a good idea to use the -k option when using
-c to insure that your messages will not be lost if part
of the shell pipeline does not function incorrectly. The
safest bet would be something like:
popclient -k -c mailgrunt | myfilter >
$HOME/filtered.mail
followed by
popclient -c mailgrunt > /dev/null
when you're sure the messages were correctly processed by
'myfilter'.
EXIT CODES
To facilitate the use of popclient in shell scripts and
the like, an exit code is returned to give an indication
of what occured during a given POP connection. The exit
code can be tested by the script and appropriate action
taken.
A simple example follows. This Bourne shell script exe-
cutes popclient and, if some messages were successfully
retrieved from a mailserver retrieved from the command
line, it starts the mail utility to read those messages.
Otherwise, it prints a brief message, and exits.
#!/bin/sh
if popclient $1 then
mail else
echo "No mail to read." fi
The exit codes returned by popclient are as follows:
0 One or more messages were successfully retrieved.
1 There was no mail awaiting retrieval.
2 An error was encountered when attempting to open a
socket for the POP connection. If you don't know
what a socket is, don't worry about it -- just
treat this as an 'unrecoverable error'.
3 The user authentication step failed. This usually
means that a bad user-id or password was specified.
4 Some sort of protocol error was detected. POP is
not especially forgiving when it comes to unex-
pected responses, commands, etc -- the protocol
invariably calls for terminating the connection
under such error conditions.
5 There was a syntax error in the arguments to pop-
client.
6 Some kind of I/O woes occurred when writing to the
local folder.
7 There was an error condition reported by the server
(POP3 only).
9 Something totally undefined occured. This is usu-
ally caused by a bug within popclient. Do let me
know if this happens.
AUTHOR
popclient was written by Carl Harris at Virginia Polytech-
nic Institute and State University (a.k.a. Virginia Tech).
BUGS
There are none! Well, maybe one or two. Send comments,
bug reports, gripes, and the like to ceharris@vt.edu.
SEE ALSO
mail(1), binmail(1), sendmail(8), popd(8), RFC 937, RFC
1225.
popclient(1L)