1milter-greylist(8) milter-greylist(8)
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6 milter-greylist - grey listing filter for sendmail
7
9 milter-greylist [-A] [-a autowhite_delay] [-c] [-D] [-d dumpfile] [-f
10 configfile] [-h] [-l] [-q] [-r] [-S] [-T] [-u username] [-v] [-w
11 greylist_delay] [-L cidrmask] [-M prefixlen] [-P pidfile] -p socket
12
14 milter-greylist is a mail filter for sendmail that implements grey
15 listing, a spam filtering technique proposed by Evan Harris.
16 Grey listing works by assuming that contrarily to legitimate MTA, spam
18 engines will not retry sending their junk mail on a temporary error.
19 The filter will always temporarily reject mail on a first attempt, and
20 accept it after some time has elapsed.
21 If spammers ever try to resend rejected messages, we can assume they
23 will not stay idle between the two sends. Odds are good that the spam‐
24 mer will send a mail to an honey pot address and get blacklisted in a
25 distributed black list before the second attempt.
26 Of course, the filter can be configured to not apply grey listing to
28 some hosts or networks. You can whitelist friendly SMTP servers, and
29 you should whitelist your own network, otherwise your SMTP clients will
30 have real trouble to send e-mail. Whitelisting localhost is also a
31 must.
32 milter-greylist works with two files. greylist.conf is the configura‐
34 tion file. It holds the whitelist of addresses that will not suffer
35 grey list filtering. It is read once upon milter-greylist startup,
36 then it will be automatically reloaded whenever a new message gets in
37 and if it had been modified. You should not send milter-greylist a kill
38 -1 as it will just terminate it (libmilter works that way).
39 See greylist.conf(5) for documentation on the file's format.
41 The second file is greylist.db. milter-greylist will regularly dump
43 its grey list database into this file, which is used on startup to
44 restore the previous grey list state. If the file does not exist or is
45 unreadable, milter-greylist will start with an empty grey list.
46 The default location for the grey list database and the socket for com‐
48 municating with sendmail is /var/milter-greylist/. That directory must
49 be owned and writeable by the user id under which milter-greylist runs.
50 The following options are available; if present, they override their
52 equivalents specified in the configuration file:
53 -A Normally, milter-greylist does not greylist senders that suc‐
55 ceeded SMTP AUTH. This option disables that feature and causes
56 authentication to be ignored. Equivalent to the noauth option
57 in the configuration file.
58 -a autowhite_delay
60 Configure auto-whitelisting. After a tuple (sender IP, sender e-
61 mail, recipient e-mail) has been accepted, other identical
62 tuples will get accepted for autowhite_delay. The default is
63 one day. Use zero to disable auto-whitelisting. A suffix can be
64 added to specify seconds (s), minutes (m), hours (h), days (d)
65 or weeks (w). Without any suffix, values are treated as seconds.
66 Equivalent to the autowhite option in the configuration file.
67 -c Only check the configuration file and exit. Return value is 0 if
69 the configuration is valid, or an error code from <sysexit.h>
70 otherwise.
71 -D Do not fork; run in the foreground instead. Without this flag,
73 milter-greylist will become a daemon. Equivalent to the node‐
74 tach option in the configuration file.
75 -d dumpfile
77 Location of the dump file. Default is /var/lib/milter-
78 greylist/db/greylist.db. Equivalent to the dumpfile option in
79 the configuration file.
80 -f configfile
82 Location of the config file. Default is /etc/mail/greylist.conf.
83 -h Show usage information.
85 -L cidrmask
87 Use cidrmask as a matching mask when checking IPv4 addresses
88 entries in the greylist. This is aimed as a workaround to mail
89 farms that re-emit messages from different IP addresses. With -L
90 24, the matching mask is 255.255.255.0, and all addresses within
91 the same class C network are considered the same. Default is -L
92 32, which corresponds to all addresses considered different.
93 -M prefixlen
95 Use prefixlen as a matching mask when checking IPv6 addresses
96 entries in the greylist. This is aimed as a workaround to mail
97 farms that re-emit messages from different IP addresses. With -M
98 64, the matching mask is ffff:ffff:ffff:ffff::, and all
99 addresses within the same subnet are considered the same.
100 Default is -M 128, which corresponds to all IPv6 addresses con‐
101 sidered different.
102 -l Enable debug output in the access-list management code.
104 -P pidfile
106 write the daemon's PID to pidfile. Equivalent to the pidfile
107 option in the configuration file.
108 -p socket
110 Use socket as the socket used by sendmail(8) to communicate with
111 milter-greylist.
112 -q Quiet mode. milter-greylist will not tell SMTP clients how much
114 time they have to wait before the message will be accepted.
115 Equivalent to the quiet option in the configuration file.
116 -r Display milter-greylist version and build environment, then
118 exit.
119 -S If milter-greylist was built with SPF support, then SPF-compli‐
121 ant senders bypass greylisting. This flag causes messages to be
122 greylisted regardless of whether they are SPF-compliant or not.
123 Equivalent to the nospf option in the configuration file.
124 -T Enable test mode. This alters the meaning of rcpt lines in
126 greylist.conf, so that only messages sent to recipient adresses
127 listed there are selected for greylisting. This option and the
128 rcpt lines have been deprecated in favor of ACL, so do not use
129 it.
130 -u username
132 Drop root privileges and switch to username credentials. Make
133 sure this user has write access to greylist.db. Equivalent to
134 the user option in the configuration file.
135 -v Enable debug output. milter-greylist will send messages (and
137 debug output if it is given the -v flag) to syslogd(8) with
138 facility LOG_MAIL. Equivalent to the verbose option in the con‐
139 figuration file.
140 -w greylist_delay
142 sets the minimum delay between the first attempt and the time
143 the message can be accepted. Default is 30 minutes. A suffix
144 can be added to specify seconds (s), minutes (m), hours (h),
145 days (d) or weeks (w). Whithout any suffix, values are treated
146 as seconds. Equivalent to the greylist option in the configura‐
147 tion file.
148
150 milter-greylist is now able to sync the greylist between multiple MX.
151 In order to enable this feature, you need to list the peer MXs in
152 greylist.conf(5) like this:
153 peer 192.0.2.17
155 peer 192.0.2.18
156 When peers are configured, milter-greylist will listen on the port
158 defined for the mxglsync service in /etc/services (defaults to 5252),
159 and it will connect to peers at this port. Each time an entry is added
160 or deleted on one MX, it will be propagated to the others.
161 The protocol is quite simple, just telnet to your MX at port 5252, and
163 type help to see how it works. Note that connections will only be
164 accepted from peer MXs, even localhost will be rejected (and don't ever
165 add localhost as a peer for MX sync, as you will cause each entry in
166 the greylist to be added twice).
167 If an MX is down, changes to the greylist will be queued until it gets
169 back up again. The queue length is limited (default is 1024 entries),
170 and if it overflows, newer entries will be discarded.
171
173 Emmanuel Dreyfus <manu@netbsd.org>
174 milter-greylist received many contributions from (in alphabetical
176 order): Aida Shinra Gary Aitken, Joel Bertrand, Moritz Both, Attila
177 Bruncsak, Pavel Cahyna, Remy Card, Alexandre Cherif, Eugene Crosser,
178 Elrond, Cyril Guibourg, Klas Heggemann, Matthieu Herrb, Dan Hollis, Per
179 Holm, Romain Kang, Guido Kerkewitz, Matt Kettler, Petr Kristof,
180 Stephane Lentz, Alexander Lobodzinski, Ivan F. Martinez, Martin Paul,
181 Christian Pelissier, Fredrik Pettai, Alexey Popov, Jeff Rife, Matthias
182 Scheler, Jobst Schmalenbach, Thomas Scheunemann, Wolfgang Solfrank,
183 Fabien Tassin, Hajimu Umemoto, Lev Walkin, and Ranko Zivojnovic
184 Thanks to Helmut Messerer and Thomas Pfau for their feedback on the
186 first releases of this software.
187
189 greylist.conf(5), sendmail(8), syslogd(8).
190 Evan Harris's paper:
192 http://projects.puremagic.com/greylisting/
193 milter-greylist's web site:
195 http://hcpnet.free.fr/milter-greylist/
196 May 10, 2005 milter-greylist(8)