man postgrey (8): 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@.*".
[email protected]: "[email protected]" 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 [email protected])

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).

Greylist Header

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.

COPYRIGHT

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 <[email protected]>