Ubuntu Manpage: milter-greylist - grey listing filter for sendmail

Provided by: milter-greylist_4.3.9-1_amd64

NAME

       milter-greylist - grey listing filter for sendmail

SYNOPSIS

       milter-greylist  [-A]  [-a  autowhite_delay]  [-c] [-D] [-d dumpfile] [-f configfile] [-h]
       [-l] [-q] [-r] [-S] [-T] [-u username[:groupname]] [-v] [-w greylist_delay] [-L  cidrmask]
       [-M prefixlen] [-P pidfile] -p socket

DESCRIPTION

milter-greylist is a mail filter for sendmail that implements grey listing, a spam
filtering technique proposed by Evan Harris.

Grey listing works by assuming that contrarily to legitimate MTA, spam engines will not
retry sending their junk mail on a temporary error. The filter will always temporarily
reject mail on a first attempt, and accept it after some time has elapsed.

If spammers ever try to resend rejected messages, we can assume they will not stay idle
between the two sends. Odds are good that the spammer will send a mail to an honey pot
address and get blacklisted in a distributed black list before the second attempt.

Of course, the filter can be configured to not apply grey listing to some hosts or
networks. You can whitelist friendly SMTP servers, and you should whitelist your own
network, otherwise your SMTP clients will have real trouble to send e-mail. Whitelisting
localhost is also a must.

milter-greylist works with two files. greylist.conf is the configuration file. It holds
the whitelist of addresses that will not suffer grey list filtering. It is read once upon
milter-greylist startup, then it will be automatically reloaded whenever a new message
gets in and if it had been modified. You should not send milter-greylist a kill -1 as it
will just terminate it (libmilter works that way).

See greylist.conf(5) for documentation on the file's format.

The second file is greylist.db. milter-greylist will regularly dump its grey list
database into this file, which is used on startup to restore the previous grey list state.
If the file does not exist or is unreadable, milter-greylist will start with an empty grey
list.

The default location for the grey list database and the socket for communicating with
sendmail is /var/milter-greylist/. That directory must be owned and writeable by the user
id under which milter-greylist runs.

The following options are available; if present, they override their equivalents specified
in the configuration file:

-A Normally, milter-greylist does not greylist senders that succeeded SMTP AUTH. This
option disables that feature and causes authentication to be ignored. Equivalent
to the noauth option in the configuration file.

-a autowhite_delay
Configure auto-whitelisting. After a tuple (sender IP, sender e-mail, recipient e-
mail) has been accepted, other identical tuples will get accepted for
autowhite_delay. The default is one day. Use zero to disable auto-whitelisting. A
suffix can be added to specify seconds (s), minutes (m), hours (h), days (d) or
weeks (w). Without any suffix, values are treated as seconds. Equivalent to the
autowhite option in the configuration file.

-c Only check the configuration file and exit. Return value is 0 if the configuration
is valid, or an error code from <sysexit.h> otherwise.

-D Do not fork; run in the foreground instead. Without this flag, milter-greylist will
become a daemon. Equivalent to the nodetach option in the configuration file.

-d dumpfile
Location of the dump file. Default is /var/milter-greylist/greylist.db. Equivalent
to the dumpfile option in the configuration file.

-f configfile
Location of the config file. Default is /etc/mail/greylist.conf.

-h Show usage information.

-L cidrmask
Use cidrmask as a matching mask when checking IPv4 addresses entries in the
greylist. This is aimed as a workaround to mail farms that re-emit messages from
different IP addresses. With -L 24, the matching mask is 255.255.255.0, and all
addresses within the same class C network are considered the same. Default is -L
32, which corresponds to all addresses considered different.

-M prefixlen
Use prefixlen as a matching mask when checking IPv6 addresses entries in the
greylist. This is aimed as a workaround to mail farms that re-emit messages from
different IP addresses. With -M 64, the matching mask is ffff:ffff:ffff:ffff::, and
all addresses within the same subnet are considered the same. Default is -M 128,
which corresponds to all IPv6 addresses considered different.

-l Enable debug output in the access-list management code.

-P pidfile
write the daemon's PID to pidfile. Equivalent to the pidfile option in the
configuration file.

-p socket
Use socket as the socket used by sendmail(8) to communicate with milter-greylist.

-q Quiet mode. milter-greylist will not tell SMTP clients how much time they have to
wait before the message will be accepted. Equivalent to the quiet option in the
configuration file.

-r Display milter-greylist version and build environment, then exit.

-S If milter-greylist was built with SPF support, then SPF-compliant senders bypass
greylisting. This flag causes messages to be greylisted regardless of whether they
are SPF-compliant or not. Equivalent to the nospf option in the configuration
file.

-T Enable test mode. This alters the meaning of rcpt lines in greylist.conf, so that
only messages sent to recipient adresses listed there are selected for greylisting.
This option and the rcpt lines have been deprecated in favor of ACL, so do not use
it.

-u username[:groupname]
Drop root privileges and switch to username (and optionally groupname) credentials.
Make sure this user (and group) has write access to greylist.db. Equivalent to the
user option in the configuration file.

-v Enable debug output. milter-greylist will send messages (and debug output if it is
given the -v flag) to syslogd(8) with facility LOG_MAIL. Equivalent to the verbose
option in the configuration file.

-w greylist_delay
sets the minimum delay between the first attempt and the time the message can be
accepted. Default is 30 minutes. A suffix can be added to specify seconds (s),
minutes (m), hours (h), days (d) or weeks (w). Whithout any suffix, values are
treated as seconds. Equivalent to the greylist option in the configuration file.

GREYLIST MX SYNC

       milter-greylist  is  now able to sync the greylist between multiple MX. In order to enable
       this feature, you need to list the peer MXs in greylist.conf(5) like this:

         peer 192.0.2.17
         peer 192.0.2.18

       When peers are configured, milter-greylist  will  listen  on  the  port  defined  for  the
       mxglsync service in /etc/services (defaults to 5252), and it will connect to peers at this
       port. Each time an entry is added or deleted on one MX,  it  will  be  propagated  to  the
       others.

       The  protocol  is  quite simple, just telnet to your MX at port 5252, and type help to see
       how it works. Note that connections will only be accepted from peer  MXs,  even  localhost
       will  be  rejected  (and don't ever add localhost as a peer for MX sync, as you will cause
       each entry in the greylist to be added twice).

       If an MX is down, changes to the greylist will be queued until it gets back up again.  The
       queue length is limited (default is 1024 entries), and if it overflows, newer entries will
       be discarded.

AUTHORS

       Emmanuel Dreyfus <manu@netbsd.org>

       milter-greylist received many contributions from (in  alphabetical  order):  Aida  Shinra,
       Adam  Katz,  Alexander  Lobodzinski, Alexandre Cherif, Alexey Popov, Andrew McGill, Attila
       Bruncsak, Benoit  Branciard,  Bernhard  Schneider,  Bob  Smith,  Constantine  A.  Murenin,
       Christian  Pelissier,  Cyril  Guibourg, Dan Hollis, Elrond, Enrico Scholz, Eugene Crosser,
       Fabien Tassin, Fredrik Pettai, Gary Aitken, Georg Horn, Gert Doering, Greg  Troxel,  Guido
       Kerkewitz,  Hajimu  Umemoto, Hideki ONO, Ivan F. Martinez, Jacques Beigbeder, Jean Benoit,
       Jeff Rife, Jobst Schmalenbach, Joe Pruett, Joel Bertrand, Johann E. Klasek, Johann Klasek,
       John Thiltges, Klas Heggemann, Laurence Moindrot, Lev Walkin, Manuel Badzong, Martin Paul,
       Matt Kettler, Mattheu Herrb, Matthias Scheler,  Matthieu  Herrb,  Michael  Fromme,  Moritz
       Both,  Nerijus  Baliunas, Pavel Cahyna, Per Holm, Petr Kristof, Ralf S. Engelschall, Ranko
       Zivojnovic, Remy Card, Rick Adams, Rogier Maas, Romain  Kang,  Rudy  Eschauzier,  Stephane
       Lentz, Thomas Scheunemann, Tim Mooney, Wolfgang Solfrank, and Yaroslav Boychuk.

       Thanks to Helmut Messerer and Thomas Pfau for their feedback on the first releases of this
       software.

NAME

SYNOPSIS

DESCRIPTION

GREYLIST MX SYNC

AUTHORS

SEE ALSO