NAME¶
postgrey - Postfix Greylisting Policy Server
SYNOPSIS¶
postgrey [
options...]
-h, --help display this help and exit
--version output version information and exit
-v, --verbose increase verbosity level
--syslog-facility Syslog facility to use (default mail)
-q, --quiet decrease verbosity level
-u, --unix=PATH listen on unix socket PATH
-i, --inet=[HOST:]PORT listen on PORT, localhost if HOST is not specified
-d, --daemonize run in the background
--pidfile=PATH put daemon pid into this file
--user=USER run as USER (default: postgrey)
--group=GROUP run as group GROUP (default: postgrey)
--dbdir=PATH put db files in PATH (default: /var/lib/postgrey)
--delay=N greylist for N seconds (default: 300)
--max-age=N delete entries older than N days since the last time
that they have been seen (default: 35)
--retry-window=N allow only N days for the first retrial (default: 2)
append 'h' if you want to specify it in hours
--greylist-action=A if greylisted, return A to Postfix (default: DEFER_IF_PERMIT)
--greylist-text=TXT response when a mail is greylisted
(default: Greylisted + help url, see below)
--lookup-by-subnet strip the last 8 bits from IP addresses (default)
--lookup-by-host do not strip the last 8 bits from IP addresses
--privacy store data using one-way hash functions
--hostname=NAME set the hostname (default: `hostname`)
--exim don't reuse a socket for more than one query (exim compatible)
--whitelist-clients=FILE default: /etc/postgrey/whitelist_clients
--whitelist-recipients=FILE default: /etc/postgrey/whitelist_recipients
--auto-whitelist-clients=N whitelist host after first successful delivery
N is the minimal count of mails before a client is
whitelisted (turned on by default with value 5)
specify N=0 to disable.
--listen-queue-size=N allow for N waiting connections to our socket
--x-greylist-header=TXT header when a mail was delayed by greylisting
default: X-Greylist: delayed <seconds> seconds by postgrey-<version> at <server>; <date>
Note that the --whitelist-x options can be specified multiple times,
and that per default /etc/postgrey/whitelist_clients.local and
/etc/postgrey/whitelist_recipients.local are also read, so that you can put
there local entries.
DESCRIPTION¶
Postgrey is a Postfix policy server implementing greylisting.
When a request for delivery of a mail is received by Postfix via SMTP, the
triplet "CLIENT_IP" / "SENDER" / "RECIPIENT" is
built. If it is the first time that this triplet is seen, or if the triplet
was first seen less than
delay seconds (300 is the default), then the
mail gets rejected with a temporary error. Hopefully spammers or viruses will
not try again later, as it is however required per RFC.
Note that you shouldn't use the --lookup-by-host option unless you know what you
are doing: there are a lot of mail servers that use a pool of addresses to
send emails, so that they can change IP every time they try again. That's why
without this option postgrey will strip the last byte of the IP address when
doing lookups in the database.
Installation¶
- •
- Create a "postgrey" user and the directory where to put the
database dbdir (default: "/var/lib/postgrey")
- •
- Write an init script to start postgrey at boot and start it. Like this for
example:
postgrey --inet=10023 -d
contrib/postgrey.init in the postgrey source distribution includes a
LSB-compliant init script by Adrian von Bidder for the Debian system.
- •
- Put something like this in /etc/main.cf:
smtpd_recipient_restrictions =
permit_mynetworks
...
reject_unauth_destination
check_policy_service inet:127.0.0.1:10023
- •
- Install the provided whitelist_clients and whitelist_recipients in
/etc/postgrey.
- •
- Put in /etc/postgrey/whitelist_recipients users that do not want
greylisting.
Whitelists¶
Whitelists allow you to specify client addresses or recipient address, for which
no greylisting should be done. Per default postgrey will read the following
files:
/etc/postgrey/whitelist_clients
/etc/postgrey/whitelist_clients.local
/etc/postgrey/whitelist_recipients
/etc/postgrey/whitelist_recipients.local
You can specify alternative paths with the --whitelist-x options.
Postgrey whitelists follow similar syntax rules as Postfix access tables. The
following can be specified for
recipient addresses:
- domain.addr
- "domain.addr" domain and subdomains.
- name@
- "name@.*" and extended addresses
"name+blabla@.*".
- name@domain.addr
- "name@domain.addr" and extended addresses.
- /regexp/
- anything that matches "regexp" (the full address is
matched).
The following can be specified for
client addresses:
- domain.addr
- "domain.addr" domain and subdomains.
- IP1.IP2.IP3.IP4
- IP address IP1.IP2.IP3.IP4. You can also leave off one number, in which
case only the first specified numbers will be checked.
- IP1.IP2.IP3.IP4/MASK
- CIDR-syle network. Example: 192.168.1.0/24
- /regexp/
- anything that matches "regexp" (the full address is
matched).
Auto-whitelisting clients¶
With the option --auto-whitelist-clients a client IP address will be
automatically whitelisted if the following conditions are met:
- •
- At least 5 successfull attempts of delivering a mail (after greylisting
was done). That number can be changed by specifying a number after the
--auto-whitelist-clients argument. Only one attempt per hour counts.
- •
- The client was last seen before --max-age days (35 per default).
Greylist Action¶
To set the action to be returned to postfix when a message fails postgrey's
tests and should be deferred, use the --greylist-action=ACTION option.
By default, postgrey returns DEFER_IF_PERMIT, which causes postfix to check the
rest of the restrictions and defer the message only if it would otherwise be
accepted. A delay action of 451 causes postfix to always defer the message
with an SMTP reply code of 451 (temp fail).
See the postfix manual page
access(5) for a discussion of the actions
allowed.
Greylist Text¶
When a message is greylisted, an error message like this will be sent at the
SMTP-level:
Greylisted, see http://postgrey.schweikert.ch/help/example.com.html
Usually no user should see that error message and the idea of that URL is to
provide some help to system administrators seeing that message or users of
broken mail clients which try to send mails directly and get a greylisting
error. Note that the default help-URL contains the original recipient domain
(example.com), so that domain-specific help can be presented to the user (on
the default page it is said to contact postmaster@example.com)
You can change the text (and URL) with the
--greylist-text parameter. The
following special variables will be replaced in the text:
- %s
- How many seconds left until the greylisting is over (300).
- %r
- Mail-domain of the recipient (example.com).
When a message is greylisted, an additional header can be prepended to the
header section of the mail:
X-Greylist: delayed %t seconds by postgrey-%v at %h; %d
You can change the text with the
--x-greylist-header parameter. The
following special variables will be replaced in the text:
- %t
- How many seconds the mail has been delayed due to greylisting.
- %v
- The version of postgrey.
- %d
- The date.
- %h
- The host.
Privacy¶
The --privacy option enable the use of a SHA1 hash function to store IPs and
emails in the greylisting database. This will defeat straight forward attempts
to retrieve mail user behaviours.
SEE ALSO¶
See <
http://www.greylisting.org/> for a description of what greylisting is
and <
http://www.postfix.org/SMTPD_POLICY_README.html> for a description
of how Postfix policy servers work.
COPYRIGHT¶
Copyright (c) 2004-2007 by ETH Zurich. All rights reserved. Copyright (c) 2007
by Open Systems AG. All rights reserved.
LICENSE¶
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 675 Mass
Ave, Cambridge, MA 02139, USA.
AUTHOR¶
David Schweikert <david@schweikert.ch>