NAME¶

mpop - A POP3 client

SYNOPSIS¶

Mail retrieval mode (default):

mpop [option...] [--] [account...]
mpop --host=host [option...]

Configuration mode:

mpop --configure <mailaddress>

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

Changing the mode of operation

Configuration options

Options specific to mail retrieval mode

USAGE¶

A suggestion for a suitable configuration file can be generated using the --configure option. The default configuration file is ~/.mpoprc or $XDG_CONFIG_HOME/mpop/config. 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.

eval cmd

Replace the current configuration file line with the first line of the output (stdout) of the command cmd. This can be used to decrypt settings or to create them via scripts. For example, eval echo host localhost replaces the current line with host localhost.
Note that every eval line will be evaluated when the configuration file is read.
Note that for passwords you can also use the passwordeval command instead of eval password cmd. This has the advantage that the command is only evaluated if needed.

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").

source_ip [IP]

Set a source IP address to bind the outgoing connection to. Useful only in special cases on multi-home systems. An empty argument disables this.

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").

socket socketname

Set the file name of a unix domain socket to connect to. This overrides both host/port and proxy_host/proxy_port.

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.

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 following command: security add-internet-password -s pop.freemail.example -r pop3 -a joe.smith -w. In both examples, replace pop.freemail.example with the POP3 server name, and joe.smith with your user name.
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 cleartext 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.
The following user / password methods are supported: user (a simple plain text method supported by all servers), plain (another simple cleartext method, supported by almost all servers), scram-sha-1 and scram-sha-1-plus (a method that avoids cleartext passwords and requires the server to prove that it is in posession of the (hashed and salted) password, which prevents some man-in-the-middle-attacks. The -plus variant additionally uses TLS channel binding information for even better security guarantees), scram-sha-256 and scram-sha-256-plus (same but with a stronger hash function), apop (an obsolete method that avoids cleartext passwords, but is not considered secure anymore), cram-md5 (an obsolete method that avoids cleartext passwords, but is not considered secure anymore), digest-md5 (an overcomplicated obsolete method that avoids cleartext passwords, but is not considered secure anymore), login (a non-standard cleartext 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).
If no method is specified, mpop will autoselect one based on security benefits. With TLS, the order is scram-sha-256-plus, scram-sha-1-plus, scram-sha-256, scram-sha-1, plain, followed by some of the obsolete methods if nothing else is available. Without TLS, only scram-sha-256 and scram-sha-1 are considered.
There are currently three authentication methods that are not based on user / password information and have to be chosen manually: oauthbearer or its predecessor xoauth2 (an OAuth2 token from the mail provider is used as the password. See the documentation of your mail provider for details on how to get this token. The passwordeval command can be used to pass the regularly changing tokens into mpop from a script or an environment variable), 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 cleartext passwords in the configuration file.

passwordeval [cmd]

Set the password for authentication to the output (stdout) of the command cmd. This can be used e.g. to decrypt password files on the fly or to query key rings, and thus to avoid storing cleartext 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.
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. The default value ist "system" and chooses the system-wide default, but you can also choose the trusted CAs yourself.
A fundamental problem with this 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.
You can also use client certificates stored on some external authentication device by specifying GnuTLS device URIs in tls_cert_file and tls_key_file. You can find the correct URIs using p11tool --list-privkeys --login (p11tool is bundled with GnuTLS). If your device requires a PIN to access the data, you can specify that using one of the password mechanisms (e.g. passwordeval, password).

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 trusted Certification Authorities (CAs). The default is the special value "system", which selects the system default. An empty argument disables trust in CAs. If you select a file, it must be in PEM format, and you should also use tls_crl_file.

tls_crl_file [file]

Deprecated. This sets a certificate revocation list (CRL) file for TLS, to check for revoked certificates (an empty argument, which is the default, disables this). Nowadays automatic OCSP checks replace CRL file checks.

tls_fingerprint [fingerprint]

Set the fingerprint of a single certificate to accept for TLS. This certificate will be trusted regardless of its contents (this overrides tls_trust_file). The fingerprint should be of type SHA256, but can for backwards compatibility also be of type SHA1 or MD5 (please avoid this). The format should be 01:23:45:67:.... Use --serverinfo --tls --tls-certcheck=off --tls-fingerprint= to get the server certificate fingerprint.

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. They are enabled by default. Disabling them will override tls_trust_file and tls_fingerprint. WARNING: When the checks are disabled, TLS sessions will not be secure!

tls_priorities [priorities]

Set priorities for TLS session parameters. The default is set by the TLS library and can be selected by using an empty argument to this command. The interpretation of the priorities string depends on the TLS library. Use --version to find out which TLS library you use.
For GnuTLS, see the section on Priority Strings in the manual.
For libtls, the priorites string is a space-separated list of parameter strings prefixed with either PROTOCOLS=, CIPHERS=, or ECDHECURVES=. These parameter strings will be passed to the functions tls_config_parse_protocols, tls_config_set_ciphers, and tls_config_set_ecdhecurves. Unrecognized parts of the priorities string will be ignored. Example: "PROTOCOLS=TLSv1.3 CIPHERS=ECDHE-RSA-AES128-SHA256 ECDHECURVES=P-384".

tls_host_override [host]

By default, TLS host verification uses the host name given by the host command. This command allows one to use a different host name for verification. This is only useful in special cases.

tls_min_dh_prime_bits [bits]

Deprecated, use tls_priorities instead. Set or unset the minimum number of Diffie-Hellman (DH) prime bits accepted 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.

delivery method method_arguments...

How to deliver messages received from this account.

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 occurred. 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. The default is to use system settings, but
# you can select your own file.
#tls_trust_file /etc/ssl/certs/ca-certificates.crt

# 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

# Use an UIDLS file in ~/.local/share instead of ~/.mpop_uidls
uidls_file ~/.local/share/%U_at_%H

# A freemail service
account freemail

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

# As an alternative to tls_trust_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 cleartext 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.

FILES¶

~/.mpoprc or $XDG_CONFIG_HOME/mpop/config

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.

SEE ALSO¶

procmail(1), spamassassin(1), netrc(5) or ftp(1), mbox(5), fcntl(2)