Ubuntu Manpage: mpop - A POP3 client

name
synopsis
description
exit status
options
usage
filtering
examples
files
environment
author
see also

NAME

       mpop - A POP3 client

SYNOPSIS

       Mail retrieval mode (default):
              mpop [option...] [--] [account...]
              mpop --host=host [option...]

       Server information mode:
              mpop [option...] --serverinfo [account...]
              mpop --host=host [option...] --serverinfo

DESCRIPTION

       In  mail  retrieval  mode  of operation, mpop retrieves mails from one or more POP3 mailboxes, optionally
       does some filtering, and delivers them through a mail delivery agent (MDA), to a maildir folder, or to an
       mbox  file.   Mails  that were successfully delivered before will not be retrieved a second time, even if
       errors occur or mpop is terminated in the middle of a session.
       In server information mode, mpop prints information about one or more POP3 servers.
       If no account names are given on the command line, one named default will be used.
       The best way to start is probably to have a look at the EXAMPLES section.

EXIT STATUS

       The standard sendmail exit codes are used, as defined in sysexits.h.

OPTIONS

       Options override configuration file settings, for every used account.

       General Options

              --version
                     Print version information, including information about the libraries used.

              --help Print help.

              -P, --pretend
                     Print the configuration settings that would be used, but do not take  further  action.   An
                     asterisk (`*') will be printed instead of your password.

              -d, --debug
                     Print  lots  of debugging information, including the whole conversation with the server. Be
                     careful with this option: the (potentially dangerous) output will  not  be  sanitized,  and
                     your password may get printed in an easily decodable format!
                     This  option  implies  --half-quiet,  because  the progress output would interfere with the
                     debugging output.

       Changing the mode of operation

              -S, --serverinfo
                     Print information about the POP3  server(s)  and  exit.  This  includes  information  about
                     supported features (pipelining, authentication methods, TOP command, ...), about parameters
                     (time for which mails will not be deleted, minimum time between logins, ...), and about the
                     TLS certificate (if TLS is active).

       Configuration options

              -C, --file=conffile
                     Use the given file instead of ~/.mpoprc as configuration file.

              --host=hostname
                     Use  this  server  with  settings  from the command line; do not use any configuration file
                     data. This option disables loading of the configuration file.  You  cannot  use  both  this
                     option and account names on the command line.

              --port=number
                     Set the port number to connect to. See the port command.

              --timeout=(off|seconds)
                     Set a network timeout. See the timeout command.

              --pipelining=(auto|on|off)
                     Enable or disable POP3 pipelining. See the pipelining command.

              --proxy-host=[IP|hostname]
                     Set or unset a SOCKS proxy to use. See the proxy_host command.

              --proxy-port=[number]
                     Set or unset a port number for the proxy host. See the proxy_port command.

              --received-header[=(on|off)]
                     Enable or disable the Received header. See the received_header command.

              --auth[=(on|method)]
                     Set the authentication method to automatic (with "on") or manually choose an authentication
                     method. See the auth command.

              --user=[username]
                     Set or unset the user name for authentication. See the user command.

              --passwordeval=[eval]
                     Evaluate password for authentication. See the passwordeval command.

              --tls[=(on|off)]
                     Enable or disable TLS/SSL. See the tls command.

              --tls-starttls[=(on|off)]
                     Enable or disable STARTTLS for TLS. See the tls_starttls command.

              --tls-trust-file=[file]
                     Set or unset a trust file for TLS. See the tls_trust_file command.

              --tls-crl-file=[file]
                     Set or unset a certificate revocation  list  (CRL)  file  for  TLS.  See  the  tls_crl_file
                     command.

              --tls-fingerprint=[fingerprint]
                     Set ot unset the fingerprint of a trusted TLS certificate. See the tls_fingerprint command.

              --tls-key-file=[file]
                     Set or unset a key file for TLS. See the tls_key_file command.

              --tls-cert-file=[file]
                     Set or unset a cert file for TLS. See the tls_cert_file command.

              --tls-certcheck[=(on|off)]
                     Enable or disable server certificate checks for TLS. See the tls_certcheck command.

              --tls-min-dh-prime-bits=[bits]
                     Set   or   unset   minimum   bit   size   of   the  Diffie-Hellmann  (DH)  prime.  See  the
                     tls_min_dh_prime_bits command.

              --tls-priorities=[priorities]
                     Set or unset TLS priorities. See the tls_priorities command.

       Options specific to mail retrieval mode

              -q, --quiet
                     Do not print status or progress information.

              -Q, --half-quiet
                     Print status but not progress information.

              -a, --all-accounts
                     Query all accounts in the configuration file.

              -A, --auth-only
                     Authenticate only; do not retrieve mail. Useful for SMTP-after-POP.

              -s, --status-only
                     Print number and size of mails in each account only; do not retrieve mail.

              -n, --only-new[=(on|off)]
                     Process only new messages. See the only_new command.

              -k, --keep[=(on|off)]
                     Do not delete mails from POP3 servers, regardless of other options or  settings.   See  the
                     keep command.

              --killsize=(off|size)
                     Set or unset kill size. See the killsize command.

              --skipsize=(off|size)
                     Set or unset skip size. See the skipsize command.

              --filter=[program]
                     Set  a  filter  which  will  decide  whether  to  retrieve,  skip,  or  delete each mail by
                     investigating the mail's headers. See the filter command.

              --delivery=method,method_arguments...
                     How to deliver messages received from this account. See the delivery command. Note  that  a
                     comma is used instead of a blank to separate the method from its arguments.

              --uidls-file=filename
                     File to store UIDLs in. See the uidls_file command.

USAGE

The default configuration file is ~/.mpoprc. Settings in this file can be changed by command line
options.
A configuration file is a simple text file. Empty lines and comment lines (first non-blank character is
'#') are ignored. Every other line must contain a command and may contain an argument to that command.
The argument may be enclosed in double quotes (").
If a file name starts with the tilde (~), this tilde will be replaced by $HOME.
If a command accepts the argument on, it also accepts an empty argument and treats that as if it was on.
Commands are organized in accounts. Each account starts with the account command and defines the settings
for one POP3 account.

Commands are as follows:

defaults
Set defaults. The following configuration commands will set default values for all following
account definitions.

account name [:account[,...]]
Start a new account definition with the given name. The current default values are filled in.
If a colon and a list of previously defined accounts is given after the account name, the new
account, with the filled in default values, will inherit all settings from the accounts in the
list.

host hostname
The POP3 server to retrieve mails from. The argument may be a host name or a network address.
Every account definition must contain this command.

port number
The port that the POP3 server listens on. The default is 110 ("pop3"), unless TLS without STARTTLS
is used, in which case it is 995 ("pop3s").

timeout (off|seconds)
Set or unset a network timeout, in seconds. The default is 180 seconds. The argument off means
that no timeout will be set, which means that the operating system default will be used.

pipelining (auto|on|off)
Enable or disable POP3 pipelining. You should never need to change the default setting, which is
auto: mpop enables pipelining for POP3 servers that advertise this capability, and disables it for
all other servers. Pipelining can speed up a POP3 session substantially.

proxy_host [IP|hostname]
Use a SOCKS proxy. All network traffic will go through this proxy host, including DNS queries,
except for a DNS query that might be necessary to resolve the proxy host name itself (this can be
avoided by using an IP address as proxy host name). An empty hostname argument disables proxy
usage. The supported SOCKS protocol version is 5. If you want to use this with Tor, see also
"Using mpop with Tor" below.

proxy_port [number]
Set the port number for the proxy host. An empty number argument resets this to the default port,
which is 1080 ("socks").

auth [(on|method)]
Choose an authentication method. The default argument on chooses a method automatically.
Usually a user name and a password are used for authentication. The user name is specified in the
configuration file with the user command. There are five different methods to specify the
password:
1. Add the password to the system key ring. Currently supported key rings are the Gnome key ring
and the Mac OS X Keychain. For the Gnome key ring, use the command secret-tool (part of Gnome's
libsecret) to store passwords: secret-tool store --label=mpop host pop.freemail.example service
pop3 user joe.smith. On Mac OS X, use the Keychain Access GUI application. The account name is
same as the user name. The keychain item name is pop3://<hostname> where <hostname> matches the
host argument.
2. Store the password in an encrypted files, and use passwordeval to specify a command to decrypt
that file, e.g. using GnuPG. See EXAMPLES.
3. Store the password in the configuration file using the password command. (Usually it is not
considered a good idea to store passwords in plain text files. If you do it anyway, you must make
sure that the file can only be read by yourself.)
4. Store the password in ~/.netrc. This method is probably obsolete.
5. Type the password into the terminal when it is required.
It is recommended to use method 1 or 2.
Multiple authentication methods exist. Most servers support only some of them. Historically,
sophisticated methods were developed to protect passwords from being sent unencrypted to the
server, but nowadays everybody needs TLS anyway, so the simple methods suffice since the whole
session is protected. A suitable authentication method is chosen automatically, and when TLS is
disabled for some reason, only methods that avoid sending clear text passwords are considered.
The following user / password methods are supported: user (a simple plain text method supported by
all servers), plain (another simple plain text method, with base64 encoding, supported by almost
all servers), scram-sha-1 (a method that avoids clear-text passwords), cram-md5 (an obsolete
method that avoids clear-text passwords), apop (an obsolete method that avoids clear-text
passwords, but is vulnerable to man-in-the-middle attacks), digest-md5 (an overcomplicated
obsolete method that avoids clear-text passwords, but is not considered secure anymore), login (a
non-standard clear-text method similar to but worse than the plain method), ntlm (an obscure non-
standard method that is now considered broken; it sometimes requires a special domain parameter
passed via ntlmdomain).
There are currently two authentication methods that are not based on user / password information
and have to be chosen manually: external (the authentication happens outside of the protocol,
typically by sending a TLS client certificate, and the method merely confirms that this
authentication succeeded), and gssapi (the Kerberos framework takes care of secure authentication,
only a user name is required).
It depends on the underlying authentication library and its version whether a particular method is
supported or not. Use --version to find out which methods are supported.

user login
Set the user name for authentication. An empty argument unsets the user name.

password secret
Set the password for authentication. An empty argument unsets the password. Consider using the
passwordeval command or a key ring instead of this command, to avoid storing plain text passwords
in the configuration file.

passwordeval [eval]
Set the password for authentication to the output (stdout) of the command eval. This can be used
e.g. to decrypt password files on the fly or to query key rings, and thus to avoid storing plain
text passwords.

ntlmdomain [domain]
Set a domain for the ntlm authentication method. This is obsolete.

tls [(on|off)]
Enable or disable TLS (also known as SSL) for secured connections. You also need tls_trust_file
or tls_fingerprint, and for some servers you may need to disable tls_starttls.
Transport Layer Security (TLS) "... provides communications privacy over the Internet. The
protocol allows client/server applications to communicate in a way that is designed to prevent
eavesdropping, tampering, or message forgery" (quote from RFC2246).
A server can use TLS in one of two modes: via a STARTTLS command (the session starts with the
normal protocol initialization, and TLS is then started using the protocol's STARTTLS command), or
immediately (TLS is initialized before the normal protocol initialization; this requires a
separate port). The first mode is the default, but you can switch to the second mode by disabling
tls_starttls.
When TLS is started, the server sends a certificate to identify itself. To verify the server
identity, a client program is expected to check that the certificate is formally correct and that
it was issued by a Certificate Authority (CA) that the user trusts. (There can also be certificate
chains with intermediate CAs.)
The list of trusted CAs is specified using the tls_trust_file command. Usually there is some
system-wide default file available, e.g. /etc/ssl/certs/ca-certificates.crt on Debian-based
systems, but you can also choose to select the trusted CAs yourself.
One practical problem with this approach is that the client program should also check if the
server certificate has been revoked for some reason, using a Certificate Revocation List (CRL). A
CRL file can be specified using the tls_crl_file command, but getting the relevant CRL files and
keeping them up to date is not straightforward. You are basically on your own.
A much more serious and fundamental problem is is that you need to trust CAs. Like any other
organization, a CA can be incompetent, malicious, subverted by bad people, or forced by government
agencies to compromise end users without telling them. All of these things happened and continue
to happen worldwide. The idea to have central organizations that have to be trusted for your
communication to be secure is fundamentally broken.
Instead of putting trust in a CA, you can choose to trust only a single certificate for the server
you want to connect to. For that purpose, specify the certificate fingerprint with
tls_fingerprint. This makes sure that no man-in-the-middle can fake the identity of the server by
presenting you a fraudulent certificate issued by some CA that happens to be in your trust list.
However, you have to update the fingerprint whenever the server certificate changes, and you have
to make sure that the change is legitimate each time, e.g. when the old certificate expired. This
is inconvenient, but it's the price to pay.
Information about a server certificate can be obtained with --serverinfo --tls
--tls-certcheck=off. This includes the issuer CA of the certificate (so you can trust that CA via
tls_trust_file), and the fingerprint of the certificate (so you can trust that particular
certificate via tls_fingerprint).
TLS also allows the server to verify the identity of the client. For this purpose, the client has
to present a certificate issued by a CA that the server trusts. To present that certificate, the
client also needs the matching key file. You can set the certificate and key files using
tls_cert_file and tls_key_file. This mechanism can also be used to authenticate users, so that
traditional user / password authentication is not necessary anymore. See the external mechanism in
auth.

tls_starttls [(on|off)]
Choose the TLS variant: start TLS from within the session (on, default), or tunnel the session
through TLS (off).

tls_trust_file file
Activate server certificate verification using a list of truted Certification Authorities (CAs).
The file must be in PEM format. Some systems provide a system-wide default file, e.g.
/etc/ssl/certs/ca-certificates.crt on Debian-based systems with the ca-certificates package. An
empty argument disables this. You should also use tls_crl_file.

tls_crl_file [file]
Set a certificate revocation list (CRL) file for TLS, to check for revoked certificates. An empty
argument disables this.

tls_fingerprint [fingerprint]
Set the fingerprint of a single certificate to accept for TLS. This certificate will be trusted
regardless of its contents. The fingerprint can be either an SHA1 (recommended) or an MD5
fingerprint in the format 01:23:45:67:.... Use --serverinfo --tls --tls-certcheck=off to get the
server certificate fingerprints.

tls_key_file file
Send a client certificate to the server (use this together with tls_cert_file}). The file must
contain the private key of a certificate in PEM format. An empty argument disables this feature.

tls_cert_file file
Send a client certificate to the server (use this together with tls_key_file). The file must
contain a certificate in PEM format. An empty argument disables this feature.

tls_certcheck [(on|off)]
Enable or disable checks of the server certificate. WARNING: When the checks are disabled, TLS
sessions will be vulnerable to man-in-the-middle attacks!

tls_min_dh_prime_bits [bits]
Set or unset the minimum number of Diffie-Hellman (DH) prime bits that mpop will accept for TLS
sessions. The default is set by the TLS library and can be selected by using an empty argument to
this command. Only lower the default (for example to 512 bits) if there is no other way to make
TLS work with the remote server.

tls_priorities [priorities]
Set the priorities for TLS sessions. The default is set by the TLS library and can be selected by
using an empty argument to this command. See the GnuTLS documentation of the gnutls_priority_init
function for a description of the priorities string.

delivery method method_arguments...
How to deliver messages received from this account.

delivery mda command
Deliver the mails through a mail delivery agent (MDA).
All occurrences of %F in the command will be replaced with the envelope from address of the
current message (or MAILER-DAEMON if none is found). Note that this address is guaranteed
to contain only letters a-z and A-Z, digits 0-9, and any of ".@_-+/", even though that is
only a subset of what is theoretically allowed in a mail address. Other characters,
including those interpreted by the shell, are replaced with "_". Nevertheless, you should
put %F into single quotes: '%F'.
Use "delivery mda /usr/bin/procmail -f '%F' -d $USER" for the procmail MDA.
Use "delivery mda /usr/sbin/sendmail -oi -oem -f '%F' -- $USER" to let your MTA handle the
mail.
Use "delivery mda /usr/local/bin/msmtp --host=localhost --from='%F' --
$USER@`hostname`.`dnsdomainname`" to pass the mail to your MTA via SMTP. (This is what
fetchmail does by default.)

delivery maildir directory
Deliver the mails to the given maildir directory. The directory must exist and it must have
the maildir subdirectories cur, new, and tmp; mpop will not create directories. This
delivery type only works on file systems that support hard links.

delivery mbox mbox-file
Deliver the mails to the given file in mbox format. The file will be locked with fcntl(2).
mpop uses the MBOXRD mbox format variant; see the documentation of the mbox format.

delivery exchange directory
Deliver the mails to the given Exchange pickup directory. The directory must exist.

If the delivery method needs to parse the mail headers for an envelope from address (the mda
method if the command contains %F, and the mbox method), then it needs to create a temporary file
to store the mail headers (but not the body) in. See $TMPDIR in the FILES / ENVIRONMENT section.

uidls_file filename
The file to store UIDLs in. These are needed to identify new messages. %U in the filename will be
replaced by the username of the current account. %H in the filename will be replaced by the
hostname of the current account. If the filename contains directories that do not exist, mpop
will create them. mpop locks this file for exclusive access when accessing the associated POP3
account.
The default value is "~/.mpop_uidls/%U_at_%H". You can also use a single UIDLS file for multiple
accounts, but then you cannot poll more than one of these accounts at the same time.

only_new [(on|off)]
By default, mpop processes only new messages (new messages are those that were not already
successfully retrieved in an earlier session). If this option is turned off, mpop will process all
messages.

keep [(on|off)]
Keep all mails on the POP3 server, never delete them. The default behaviour is to delete mails
that have been successfully retrieved or filtered by kill filters.

killsize (off|size)
Mails larger than the given size will be deleted (unless the keep command is used, in which case
they will just be skipped). The size argument must be zero or greater. If it is followed by a `k'
or an `m', the size is measured in kibibytes/mebibytes instead of bytes. Note that some POP3
servers report slightly incorrect sizes for mails; see NOTES below.
When killsize is set to 0 and keep is set to on, then all mails are marked as retrieved, but no
mail gets deleted from the server. This can be used to synchronize the UID list on the client to
the UID list on the server.

skipsize (off|size)
Mails larger than the given size will be skipped (not downloaded). The size argument must be zero
or greater. If it is followed by a `k' or an `m', the size is measured in kibibytes/mebibytes
instead of bytes. Note that some POP3 servers report slightly incorrect sizes for mails; see
NOTES below.

filter [command]
Set a filter which will decide whether to retrieve, skip, or delete each mail by investigating the
mail's headers. The POP3 server must support the POP3 TOP command for this to work; see option
--serverinfo above. An empty argument disables filtering.
All occurrences of %F in the command will be replaced with the envelope from address of the
current message (or MAILER-DAEMON if none is found). Note that this address is guaranteed to
contain only letters a-z and A-Z, digits 0-9, and any of ".@_-+/", even though that is only a
subset of what is theoretically allowed in a mail address. Other characters, including those
interpreted by the shell, are replaced with "_". Nevertheless, you should put %F into single
quotes: '%F'.
All occurrences of %S in the command will be replaced with the size of the current mail as
reported by the POP3 server.
The mail headers (plus the blank line separating the headers from the body) will be piped to the
command. Based on the return code, mpop decides what to do with the mail:
0: proceed normally; no special action
1: delete the mail; do not retrieve it
2: skip the mail; do not retrieve it
Return codes greater than or equal to 3 mean that an error occured. The sysexits.h error codes may
be used to give information about the kind of the error, but this is not necessary.

received_header [(on|off)]
Enable or disable adding a Received header. By default, mpop prepends a Received header to the
mail during delivery. This is required by the RFCs if the mail is subsequently further delivered
e.g. via SMTP.

FILTERING

       There are three filtering commands available.  They will be executed in the following order:
       killsize
       skipsize
       filter
       If a filtering command applies to a mail, the remaining filters will not be executed.

EXAMPLES

Configuration file

# Example for a user configuration file ~/.mpoprc
#
# This file focusses on TLS, authentication, and the mail delivery method.
# Features not used here include mail filtering, timeouts, SOCKS proxies,
# TLS parameters, and more.

# Set default values for all following accounts.
defaults

# Always use TLS.
tls on

# Set a list of trusted CAs for TLS. You can use a system-wide default file,
# as in this example, or download the root certificate of your CA and use that.
tls_trust_file /etc/ssl/certs/ca-certificates.crt

# Additionally, you should use the tls_crl_file command to check for revoked
# certificates, but unfortunately getting revocation lists and keeping them
# up to date is not straightforward.
#tls_crl_file ~/.tls-crls

# Deliver mail to an MBOX mail file:
delivery mbox ~/Mail/inbox
# Deliver mail to a maildir folder:
#delivery maildir ~/Mail/incoming
# Deliver mail via procmail:
#delivery mda "/usr/bin/procmail -f '%F' -d $USER"
# Deliver mail via the local SMTP server:
#delivery mda "/usr/bin/msmtp --host=localhost --from='%F' -- $USER"
# Deliver mail to an Exchange pickup directory:
#delivery exchange c:\exchange\pickup

# A freemail service
account freemail

# Host name of the POP3 server
host pop.freemail.example

# As an alternative to tls_trust_file/tls_crl_file, you can use tls_fingerprint
# to pin a single certificate. You have to update the fingerprint when the
# server certificate changes, but an attacker cannot trick you into accepting
# a fraudulent certificate. Get the fingerprint with
# $ mpop --serverinfo --tls --tls-certcheck=off --host=pop.freemail.example
tls_fingerprint 00:11:22:33:44:55:66:77:88:99:AA:BB:CC:DD:EE:FF:00:11:22:33

# Authentication. The password is given using one of five methods, see below.
user joe.smith

# Password method 1: Add the password to the system keyring, and let mpop get
# it automatically. To set the keyring password using Gnome's libsecret:
# $ secret-tool store --label=mpop \
# host pop.freemail.example \
# service pop3 \
# user joe.smith

# Password method 2: Store the password in an encrypted file, and tell mpop
# which command to use to decrypt it. This is usually used with GnuPG, as in
# this example. Usually gpg-agent will ask once for the decryption password.
passwordeval gpg2 --no-tty -q -d ~/.mpop-password.gpg

# Password method 3: Store the password directly in this file. Usually it is not
# a good idea to store passwords in plain text files. If you do it anyway, at
# least make sure that this file can only be read by yourself.
#password secret123

# Password method 4: Store the password in ~/.netrc. This method is probably not
# relevant anymore.

# Password method 5: Do not specify a password. Mpop will then prompt you for
# it. This means you need to be able to type into a terminal when mpop runs.

# A second mail box at the same freemail service
account freemail2 : freemail
user joey

# The POP3 server of your ISP
account isp
host mail.isp.example
auth on
user 12345
# Your ISP runs SpamAssassin, so test each mail for the "X-Spam-Status: Yes"
# header, and delete all mails with this header before downloading them.
filter if [ "`grep "^X-Spam-Status: Yes"`" ]; then exit 1; else exit 0; fi

# Set a default account
account default : freemail

Filtering with SpamAssassin

The command filter "/path/to/spamc -c > /dev/null" will delete all mails that SpamAssassin thinks are
spam. Since no message body is passed to SpamAssassin, you should disable all body-specific tests in the
SpamAssassin configuration file; for example set use_bayes 0.

If your mail provider runs SpamAssassin for you, you just have to check for the result. The following
script can do that when used as an mpop filter:
#!/bin/sh
if [ "`grep "^X-Spam-Status: Yes"`" ]; then
exit 1 # kill this message
else
exit 0 # proceed normally
fi
Since the filter command is passed to a shell, you can also use this directly:
filter if [ "`grep "^X-Spam-Status: Yes"`" ]; then exit 1; else exit 0; fi

Using mpop with Tor

Use the following settings:
proxy_host 127.0.0.1
proxy_port 9050
tls on
Use an IP address as proxy host name, so that mpop does not leak a DNS query when resolving it.
TLS is required to prevent exit hosts from reading your POP3 session. You also need tls_trust_file or
tls_fingerprint to check the server identity.

FILES

       ~/.mpoprc
              Default configuration file.

       ~/.mpop_uidls
              Default directory to store UIDLs files in.

       ~/.netrc and SYSCONFDIR/netrc
              The  netrc  file contains login information. Before prompting for a password, msmtp will search it
              in ~/.netrc and SYSCONFDIR/netrc.

ENVIRONMENT

       $USER, $LOGNAME
              These variables override the user's login name. $LOGNAME is only  used  if  $USER  is  unset.  The
              user's login name is used for Received headers.

       $TMPDIR
              Directory  to  create temporary files in. If this is unset, a system specific default directory is
              used.

AUTHOR

       mpop was written by Martin Lambers <marlam@marlam.de>
       Other authors are listed in the AUTHORS file in the source distribution.