NAME
postfwd - postfix firewall daemon
SYNOPSIS
postfwd [OPTIONS] [SOURCE1, SOURCE2, ...]
Ruleset: (at least one, multiple use is allowed):
-f, --file <file> reads rules from <file>
-r, --rule <rule> adds <rule> to config
Scoring:
-s, --scores <v>=<r> returns <r> when score exceeds <v>
Networking:
-d, --daemon run postfwd as daemon
-i, --interface <dev> listen on interface <dev>
-p, --port <port> listen on port <port>
--proto <proto> socket type (tcp or unix)
-u, --user <name> set uid to user <name>
-g, --group <name> set gid to group <name>
-R, --chroot <path> chroot the daemon to <path>
--pidfile <path> create pidfile under <path>
-l, --logname <label> label for syslog messages
--loglen <int> truncates syslogs after <int> chars
Caching:
-c, --cache <int> sets the request-cache timeout to <int> seconds
--cache-no-size ignores size attribute for caching
--cache-no-sender ignores sender address in cache
--cache-rdomain-only ignores localpart of recipient address in cache
--cache-rbl-timeout default rbl timeout, if not specified in ruleset
--cache-rbl-default default rbl response pattern to match (regexp)
--cacheid <item>, .. list of attributes for request cache identifier
--cleanup-requests cleanup interval in seconds for request cache
--cleanup-rbls cleanup interval in seconds for rbl cache
--cleanup-rates cleanup interval in seconds for rate cache
Optional:
-t, --test testing, always returns "dunno"
-v, --verbose verbose logging, use twice (-vv) to increase level
-S, --summary <int> show some usage statistics every <int> seconds
--norulelog disbles rule logging
--norulestats disables per rule statistics
--noidlestats disables statistics when idle
-n, --nodns disable dns
--nodnslog disable dns logging
--dns_async_txt perform dnsbl A and TXT lookups simultaneously
--dns_timeout timeout in seconds for asynchonous dns queries
--dns_timeout_max maximum of dns timeouts until a dnsbl will be deactivated
--dns_timeout_interval interval in seconds for dns timeout maximum counter
--dns_max_ns_lookups max names to look up with sender_ns_addrs
--dns_max_mx_lookups max names to look up with sender_mx_addrs
-I, --instantcfg re-reads rulefiles for every new request
--config_timeout <i> parser timeout in seconds
Informational (use only at command-line!):
-C, --showconfig shows ruleset summary, -v for verbose
-L, --stdoutlog redirect syslog messages to stdout
-P, --perfmon no syslogging, no stdout
-V, --version shows program version
-h, --help shows usage
-m, --manual shows program manual
Plugins:
--plugins <file> loads plugins from <file>
DESCRIPTION
INTRODUCTION
postfwd is written to combine complex postfix restrictions in a ruleset
similar to those of the most firewalls. The program uses the postfix
policy delegation protocol to control access to the mail system before
a message has been accepted (please visit
<http://www.postfix.org/SMTPD_POLICY_README.html> for more
information).
postfwd allows you to choose an action (e.g. reject, dunno) for a
combination of several smtp parameters (like sender and recipient
address, size or the client’s TLS fingerprint). Also it offers simple
macros/acls which should allow straightforward and easy-to-read
configurations.
Features:
* Complex combinations of smtp parameters
* Combined RBL/RHSBL lookups with arbitrary actions depending on
results
* Scoring system
* Date/time based rules
* Macros/ACLs, Groups, Negation
* Compare request attributes (e.g. client_name and helo_name)
* Internal caching for requests and dns lookups
* Built in statistics for rule efficiency analysis
CONFIGURATION
A configuration line consists of optional item=value pairs, separated
by semicolons (‘;‘) and the appropriate desired action:
[ <item1>[=><~]=<value>; <item2>[=><~]=<value>; ... ] action=<result>
Example:
client_address=192.168.1.1 ; sender==no@bad.local ; action=REJECT
This will deny all mail from 192.168.1.1 with envelope sender
no@bad.local. The order of the elements is not important. So the
following would lead to the same result as the previous example:
action=REJECT ; client_address=192.168.1.1 ; sender==no@bad.local
The way how request items are compared to the ruleset can be influenced
in the following way:
====================================================================
ITEM == VALUE true if ITEM equals VALUE
ITEM => VALUE true if ITEM >= VALUE
ITEM =< VALUE true if ITEM <= VALUE
ITEM =~ VALUE true if ITEM ~= /^VALUE$/i
ITEM != VALUE false if ITEM equals VALUE
ITEM !> VALUE false if ITEM >= VALUE
ITEM !< VALUE false if ITEM <= VALUE
ITEM !~ VALUE false if ITEM ~= /^VALUE$/i
ITEM = VALUE default behaviour (see ITEMS section)
====================================================================
To identify single rules in your log files, you may add an unique
identifier for each of it:
id=R_001 ; action=REJECT ; client_address=192.168.1.1 ; sender==no@bad.local
You may use these identifiers as target for the ‘jump()‘ command (see
ACTIONS section below). Leading or trailing whitespace characters will
be ignored. Use ’#’ to comment your configuration. Others will
appreciate.
A ruleset consists of one or multiple rules, which can be loaded from
files or passed as command line arguments. Please see the COMMAND LINE
section below for more information on this topic.
Rules can span multiple lines by adding a trailing backslash "\"
character:
id=R_001 ; client_address=192.168.1.0/24; sender==no@bad.local; \
action=REJECT please use your relay from there
ITEMS
id - a unique rule id, which can be used for log analysis
ids also serve as targets for the "jump" command.
date, time - a time or date range within the specified rule shall hit
# FORMAT:
# Feb, 29th
date=29.02.2008
# Dec, 24th - 26th
date=24.12.2008-26.12.2008
# from today until Nov, 23rd
date=-23.09.2008
# from April, 1st until today
date=01.04.2008-
days, months - a range of weekdays (Sun-Sat) or months (Jan-Dec)
within the specified rule shall hit
score - when the specified score is hit (see ACTIONS section)
the specified action will be returned to postfix
scores are set global until redefined!
request_score - this value allows to access a request’s score. it
may be used as variable ($$request_score).
rbl, rhsbl, - query the specified RBLs/RHSBLs, possible values are:
rhsbl_client, <name>[/<reply>/<maxcache>, <name>/<reply>/<maxcache>]
rhsbl_sender, (defaults: reply=^127\.0\.0\.\d+$ maxcache=3600)
rhsbl_reverse_client the results of all rhsbl_* queries will be combined
in rhsbl_count (see below).
rblcount, rhsblcount - minimum RBL/RHSBL hitcounts to match. if not specified
a single RBL/RHSBL hit will match the rbl/rhsbl items.
you may specify ’all’ to evaluate all items, and use
it as variable in an action (see ACTIONS section)
(default: 1)
sender_localpart, - the local-/domainpart of the sender address
sender_domain
recipient_localpart, - the local-/domainpart of the recipient address
recipient_domain
helo_address - postfwd tries to look up the helo_name. use
helo_address=!!(0.0.0.0/0) to check for unknown.
Please do not use this for positive access control
(whitelisting), as it might be forged.
sender_ns_names, - postfwd tries to look up the names/ip addresses
sender_ns_addrs of the nameservers for the sender domain part.
Please do not use this for positive access control
(whitelisting), as it might be forged.
sender_mx_names, - postfwd tries to look up the names/ip addresses
sender_mx_addrs of the mx records for the sender domain part.
Please do not use this for positive access control
(whitelisting), as it might be forged.
version - postfwd version, contains "postfwd n.nn"
this enables version based checks in your rulesets
(e.g. for migration). works with old versions too,
because a non-existing item always returns false:
id=R01; version~=1.10; sender_domain==some.org \
; action=REJECT sorry no access
Besides these you can specify any attribute of the postfix policy
delegation protocol. Feel free to combine them the way you need it
(have a look at the EXAMPLES section below).
Most values can be specified as regular expressions (PCRE). Please see
the table below for details:
# ==========================================================
# ITEM=VALUE TYPE
# ==========================================================
id=something mask = string
date=01.04.2007-22.04.2007 mask = date (DD.MM.YYYY-DD.MM.YYYY)
time=08:30:00-17:00:00 mask = time (HH:MM:SS-HH:MM:SS)
days=Mon-Wed mask = weekdays (Mon-Wed) or numeric (1-3)
months=Feb-Apr mask = months (Feb-Apr) or numeric (1-3)
score=5.0 mask = maximum floating point value
rbl=zen.spamhaus.org mask = <name>/<reply>/<maxcache>[,...]
rblcount=2 mask = numeric, will match if rbl hits >= 2
helo_address=<a.b.c.d/nn> mask = CIDR[,CIDR,...]
sender_ns_names=some.domain.tld mask = PCRE
sender_mx_names=some.domain.tld mask = PCRE
sender_ns_addrs=<a.b.c.d/nn> mask = CIDR[,CIDR,...]
sender_mx_addrs=<a.b.c.d/nn> mask = CIDR[,CIDR,...]
# ------------------------------
# Postfix version 2.1 and later:
# ------------------------------
client_address=<a.b.c.d/nn> mask = CIDR[,CIDR,...]
client_name=another.domain.tld mask = PCRE
reverse_client_name=another.domain.tld mask = PCRE
helo_name=some.domain.tld mask = PCRE
sender=foo@bar.tld mask = PCRE
recipient=bar@foo.tld mask = PCRE
recipient_count=5 mask = numeric, will match if recipients >= 5
# ------------------------------
# Postfix version 2.2 and later:
# ------------------------------
sasl_method=plain mask = PCRE
sasl_username=you mask = PCRE
sasl_sender= mask = PCRE
size=12345 mask = numeric, will match if size >= 12345
ccert_subject=blackhole.nowhere.local mask = PCRE (only if tls verified)
ccert_issuer=John+20Doe mask = PCRE (only if tls verified)
ccert_fingerprint=AA:BB:CC:DD:EE:... mask = PCRE (do NOT use "..." here)
# ------------------------------
# Postfix version 2.3 and later:
# ------------------------------
encryption_protocol=TLSv1/SSLv3 mask = PCRE
encryption_cipher=DHE-RSA-AES256-SHA mask = PCRE
encryption_keysize=256 mask = numeric, will match if keysize >= 256
...
the current list can be found at
<http://www.postfix.org/SMTPD_POLICY_README.html>. Please read
carefully about which attribute can be used at which level of the smtp
transaction (e.g. size will only work reliably at END_OF_DATA level).
Pattern matching is performed case insensitive.
Multiple use of the same item is allowed and will compared as logical
OR, which means that this will work as expected:
id=TRUST001; action=OK; encryption_keysize=64; \
ccert_fingerprint=11:22:33:44:55:66:77:88:99; \
ccert_fingerprint=22:33:44:55:66:77:88:99:00; \
ccert_fingerprint=33:44:55:66:77:88:99:00:11; \
sender=@domain\.local$
client_address, rbl and rhsbl items may also be specified as
whitespace-or-comma-separated values:
id=SKIP01; action=dunno; \
client_address=192.168.1.0/24, 172.16.254.23
id=SKIP02; action=dunno; \
client_address= 10.10.3.32 \
10.216.222.0/27
The following items currently have to be unique:
id, minimum and maximum values, rblcount and rhsblcount
Any item can be negated by preceeding ’!!’ to it, e.g.:
id=TLS001 ; hostname=!!^secure\.trust\.local$ ; action=REJECT only secure.trust.local please
or using the right compare operator:
id=USER01 ; sasl_username !~ /^(bob│alice)$/ ; action=REJECT who is that?
To avoid confusion with regexps or simply for better visibility you can
use ’!!(...)’:
id=USER01 ; sasl_username=!!( (bob│alice) ) ; action=REJECT who is that?
Request attributes can be compared by preceeding ’$$’ characters, e.g.:
id=R-003 ; client_name = !! $$helo_name ; action=WARN helo does not match DNS
# or
id=R-003 ; client_name = !!($$(helo_name)) ; action=WARN helo does not match DNS
This is only valid for PCRE values (see list above). The comparison
will be performed as case insensitive exact match. Use the ’-vv’
option to debug.
FILES
Since postfwd1 v1.15 and postfwd2 v0.18 long item lists can be stored
in separate files:
id=R001 ; ccert_fingerprint==file:/etc/postfwd/wl_ccerts ; action=DUNNO
postfwd will read a list of items (one item per line) from
/etc/postfwd/wl_ccerts. comments are allowed:
# client1
11:22:33:44:55:66:77:88:99
# client2
22:33:44:55:66:77:88:99:00
# client3
33:44:55:66:77:88:99:00:11
To use existing tables in key=value format, you can use:
id=R001 ; ccert_fingerprint==table:/etc/postfwd/wl_ccerts ; action=DUNNO
This will ignore the right-hand value. Items can be mixed:
id=R002 ; action=REJECT \
client_name==unknown; \
client_name==file:/etc/postfwd/blacklisted
and for non pcre (comma separated) items:
id=R003 ; action=REJECT \
client_address==10.1.1.1, file:/etc/postfwd/blacklisted
id=R004 ; action=REJECT \
rbl=myrbl.home.local, zen.spamhaus.org, file:/etc/postfwd/rbls_changing
You can check your configuration with the --show_config option at the
command line:
# postfwd --showconfig --rule=’action=DUNNO; client_address=10.1.0.0/16, file:/etc/postfwd/wl_clients, 192.168.2.1’
should give something like:
Rule 0: id->"R-0"; action->"DUNNO"; client_address->"=;10.1.0.0/16, =;194.123.86.10, =;186.4.6.12, =;192.168.2.1"
If a file can not be read, it will be ignored:
# postfwd --showconfig --rule=’action=DUNNO; client_address=10.1.0.0/16, file:/etc/postfwd/wl_clients, 192.168.2.1’
[LOG warning]: error: file /etc/postfwd/wl_clients not found - file will be ignored ?
Rule 0: id->"R-0"; action->"DUNNO"; client_address->"=;10.1.0.0/16, =;192.168.2.1"
File items are evaluated at configuration stage. Therefore postfwd
needs to be reloaded if a file has changed.
If you want to specify a file, that will be reloaded for each request,
you can use lfile: and ltable:
id=R001; client_address=lfile:/etc/postfwd/client_whitelist; action=dunno
This will check the modification time of /etc/postfwd/client_whitelist
every time the rule is evaluated and reload it as necessary. Of course
this might increase the system load, so please use it with care.
The --showconfig option illustrates the difference:
## evaluated at configuration stage
# postfwd2 --nodaemon -L --rule=’client_address=table:/etc/postfwd/clients; action=dunno’ -C
Rule 0: id->"R-0"; action->"dunno"; client_address->"=;1.1.1.1, =;1.1.1.2, =;1.1.1.3"
## evaluated for any rulehit
# postfwd2 --nodaemon -L --rule=’client_address=ltable:/etc/postfwd/clients; action=dunno’ -C
Rule 0: id->"R-0"; action->"dunno"; client_address->"=;ltable:/etc/postfwd/clients"
Files can refer to other files. The following is valid.
-- FILE /etc/postfwd/rules.cf --
id=R001; client_address=file:/etc/postfwd/clients_master.cf; action=DUNNO
-- FILE /etc/postfwd/clients_master.cf --
192.168.1.0/24
file:/etc/postfwd/clients_east.cf
file:/etc/postfwd/clients_west.cf
-- FILE /etc/postfwd/clients_east.cf --
192.168.2.0/24
-- FILE /etc/postfwd/clients_west.cf --
192.168.3.0/24
Remind that there is currently no loop detection (/a/file calls
/a/file) and that this feature is only available with postfwd1 v1.15
and postfwd2 v0.18 and higher.
ACTIONS
General
Actions will be executed, when all rule items have matched a request
(or at least one of any item list). You can refer to request attributes
by preceeding $$ characters, like:
id=R-003; client_name = !!$$helo_name; action=WARN helo ’$$helo_name’ does not match DNS ’$$client_name’
# or
id=R-003; client_name = !!$$helo_name; action=WARN helo ’$$(helo_name)’ does not match DNS ’$$(client_name)’
postfix actions
Actions will be replied to postfix as result to policy delegation
requests. Any action that postfix understands is allowed - see "man 5
access" or <http://www.postfix.org/access.html> for a description. If
no action is specified, the postfix WARN action which simply logs the
event will be used for the corresponding rule.
postfwd will return dunno if it has reached the end of the ruleset and
no rule has matched. This can be changed by placing a last rule
containing only an action statement:
...
action=dunno ; sender=@domain.local # sender is ok
action=reject # default deny
postfwd actions
postfwd actions control the behaviour of the program. Currently you can
specify the following:
jump (<id>)
jumps to rule with id <id>, use this to skip certain rules.
you can jump backwards - but remember that there is no loop
detection at the moment! jumps to non-existing ids will be skipped.
score (<score>)
the request’s score will be modified by the specified <score>,
which must be a floating point value. the modificator can be either
+n.nn adds n.nn to current score
-n.nn sustracts n.nn from the current score
*n.nn multiplies the current score by n.nn
/n.nn divides the current score through n.nn
=n.nn sets the current score to n.nn
if the score exceeds the maximum set by ‘--scores‘ option (see
COMMAND LINE) or the score item (see ITEMS section), the action
defined for this case will be returned (default: 5.0=>"REJECT postfwd score exceeded").
set (<item>=<value>,<item>=<value>,...)
this command allows you to insert or override request attributes, which then may be
compared to your further ruleset. use this to speed up repeated comparisons to large item lists.
please see the EXAMPLES section for more information. you may separate multiple key=value pairs
by "," characters.
rate (<item>/<max>/<time>/<action>)
this command creates a counter for the given <item>, which will be increased any time a request
containing it arrives. if it exceeds <max> within <time> seconds it will return <action> to postfix.
rate counters are very fast as they are executed before the ruleset is parsed.
# no more than 3 requests per 5 minutes
# from the same "unknown" client
id=RATE01 ; client_name==unknown ; \
action==rate($$client_address/3/300/450 4.7.1 sorry, max 3 requests per 5 minutes)
size (<item>/<max>/<time>/<action>)
this command works similar to the rate() command with the difference, that the rate counter is
increased by the request’s size attribute. to do this reliably you should call postfwd from
smtpd_end_of_data_restrictions. if you want to be sure, you could check it within the ruleset:
# size limit 1.5mb per hour per client
id=SIZE01 ; state==END_OF_DATA ; client_address==!!(10.1.1.1); \
action==size($$client_address/1572864/3600/450 4.7.1 sorry, max 1.5mb per hour)
rcpt (<item>/<max>/<time>/<action>)
this command works similar to the rate() command with the difference, that the rate counter is
increased by the request’s recipient_count attribute. to do this reliably you should call postfwd
from smtpd_data_restrictions or smtpd_end_of_data_restrictions. if you want to be sure, you could
check it within the ruleset:
# recipient count limit 3 per hour per client
id=RCPT01 ; state==END_OF_DATA ; client_address==!!(10.1.1.1); \
action==rcpt($$client_address/3/3600/450 4.7.1 sorry, max 3 recipients per hour)
ask (<addr>:<port>[:<ignore>])
allows to delegate the policy decision to another policy service (e.g. postgrey). the first
and the second argument (address and port) are mandatory. a third optional argument may be
specified to tell postfwd to ignore certain answers and go on parsing the ruleset:
# example1: query postgrey and return it’s answer to postfix
id=GREY; client_address==10.1.1.1; action=ask(127.0.0.1:10031)
# example2: query postgrey but ignore it’s answer, if it matches ’DUNNO’
# and continue parsing postfwd’s ruleset
id=GREY; client_address==10.1.1.1; action=ask(127.0.0.1:10031:^dunno$)
wait (<delay>)
pauses the program execution for <delay> seconds. use this for
delaying or throtteling connections.
note (<string>)
just logs the given string and continues parsing the ruleset.
if the string is empty, nothing will be logged.
quit (<code>)
terminates the program with the given exit-code. postfix doesn‘t
like that too much, so use it with care.
You can reference to request attributes, like
id=R-HELO ; helo_name=^[^\.]+$ ; action=REJECT invalid helo ’$$helo_name’
These special attributes will be reset for any new rule:
rblcount - contains the number of RBL answers
rhsblcount - contains the number of RHSBL answers
matches - contains the number of matched items
dnsbltext - contains the dns TXT part of all RBL and RHSBL replies in the form
rbltype:rblname:<txt>; rbltype:rblname:<txt>; ...
These special attributes will be changed for any matching rule:
request_hits - contains ids of all matching rules
This means that it might be necessary to save them, if you plan to use
these values in later rules:
# set vals
id=RBL01 ; rhsblcount=all ; rblcount=all ; \
rbl=list.dsbl.org, bl.spamcop.net, dnsbl.sorbs.net, zen.spamhaus.org ; \
rhsbl_client=rddn.dnsbl.net.au, rhsbl.ahbl.org, rhsbl.sorbs.net ; \
rhsbl_sender=rddn.dnsbl.net.au, rhsbl.ahbl.org, rhsbl.sorbs.net ; \
action=set(HIT_rhls=$$rhsblcount,HIT_rbls=$$rblcount,HIT_txt=$$dnsbltext)
# compare
id=RBL02 ; HIT_rhls>=1 ; HIT_rbls>=1 ; action=554 5.7.1 blocked using $$HIT_rhls RHSBLs and $$HIT_rbls RBLs [INFO: $$HIT_txt]
id=RBL03 ; HIT_rhls>=2 ; action=554 5.7.1 blocked using $$HIT_rhls RHSBLs [INFO: $$HIT_txt]
id=RBL04 ; HIT_rbls>=2 ; action=554 5.7.1 blocked using $$HIT_rbls RBLs [INFO: $$HIT_txt]
MACROS/ACLS
Multiple use of long items or combinations of them may be abbreviated
by macros. Those must be prefixed by ’&&’ (two ’&’ characters). First
the macros have to be defined as follows:
&&RBLS { rbl=zen.spamhaus.org,list.dsbl.org,bl.spamcop.net,dnsbl.sorbs.net,ix.dnsbl.manitu.net; };
Then these may be used in your rules, like:
&&RBLS ; client_name=^unknown$ ; action=REJECT
&&RBLS ; client_name=(\d+[\.-_]){4} ; action=REJECT
&&RBLS ; client_name=[\.-_](adsl│dynamic│ppp│)[\.-_] ; action=REJECT
Macros can contain actions, too:
# definition
&&GONOW { action=REJECT your request caused our spam detection policy to reject this message. More info at http://www.domain.local; };
# rules
&&GONOW ; &&RBLS ; client_name=^unknown$
&&GONOW ; &&RBLS ; client_name=(\d+[\.-_]){4}
&&GONOW ; &&RBLS ; client_name=[\.-_](adsl│dynamic│ppp│)[\.-_]
Macros can contain macros, too:
# definition (note the trailing "\" characters)
&&RBLS { \
rbl=zen.spamhaus.org ; \
rbl=list.dsbl.org ; \
rbl=bl.spamcop.net ; \
rbl=dnsbl.sorbs.net ; \
rbl=ix.dnsbl.manitu.net ; \
};
&&DYNAMIC { \
client_name=^unknown$ ; \
client_name=(\d+[\.-_]){4} ; \
client_name=[\.-_](adsl│dynamic│ppp│)[\.-_] ; \
};
&&GOAWAY { &&RBLS; &&DYNAMIC; };
# rules
&&GOAWAY ; action=REJECT dynamic client and listed on RBL
Basically macros are simple text substitutions - see the "PARSER"
section for more information.
PLUGINS
Please visit <http://www.postfwd.org/postfwd.plugins>
COMMAND LINE
Ruleset
The following arguments are used to specify the source of the postfwd
ruleset. This means that at least one of the following is required for
postfwd to work.
-f, --file <file>
Reads rules from <file>. Please see the CONFIGURATION section
below for more information.
-r, --rule <rule>
Adds <rule> to ruleset. Remember that you might have to quote
strings that contain whitespaces or shell characters.
Plugins
--plugins
A file containing plugin routines for postfwd. Please see the
PLUGINS section for more information.
Scoring
-s, --scores <val>=<action>
Returns <action> to postfix, when the request’s score exceeds <val>
Multiple usage is allowed. Just chain your arguments, like:
postfwd -r "<item>=<value>;action=<result>" -f <file> -f <file> --plugins <file> ...
or
postfwd --scores 4.5="WARN high score" --scores 5.0="REJECT postfwd score too high" ...
In case of multiple scores, the highest match will count. The order of
the arguments will be reflected in the postfwd ruleset.
Networking
postfwd can be run as daemon so that it listens on the network for
incoming requests. The following arguments will control it’s behaviour
in this case.
-d, --daemon
postfwd will run as daemon and listen on the network for incoming
queries (default 127.0.0.1:10040).
-i, --interface <dev>
Bind postfwd to the specified interface (default 127.0.0.1).
-p, --port <port>
postfwd listens on the specified port (default tcp/10040).
--proto <type>
The protocol type for postfwd’s socket. Currently you may use ’tcp’ or ’unix’ here.
To use postfwd with a unix domain socket, run it as follows:
postfwd --proto=unix --port=/somewhere/postfwd.socket
-u, --user <name>
Changes real and effective user to <name>.
-g, --group <name>
Changes real and effective group to <name>.
-R, --chroot <path>
Chroot the process to the specified path.
Test this before using - you might need some libs there.
--pidfile <path>
The process id will be saved in the specified file.
-l, --logname <label>
Labels the syslog messages. Useful when running multiple
instances of postfwd.
--loglen <int>
Truncates any syslog message after <int> characters.
Optional arguments
These parameters influence the way postfwd is working. Any of them can
be combined.
-v, --verbose
Verbose logging displays a lot of useful information but can cause
your logfiles to grow noticeably. So use it with caution. Set the option
twice (-vv) to get more information (logs all request attributes).
-c, --cache <int> (default=600)
Timeout for request cache, results for identical requests will be
cached until config is reloaded or this time (in seconds) expired.
A setting of 0 disables this feature.
--cache-no-size
Ignores size attribute for cache comparisons which will lead to better
cache-hit rates. You should set this option, if you don’t use the size
item in your ruleset.
--cache-no-sender
Ignores sender address for cache comparisons which will lead to better
cache-hit rates. You should set this option, if you don’t use the sender
item in your ruleset.
--cache-rdomain-only
This will strip the localpart of the recipient’s address before filling the
cache. This may considerably increase cache-hit rates.
--cache-rbl-timeout <timeout> (default=3600)
This default value will be used as timeout in seconds for rbl cache items,
if not specified in the ruleset.
--cache-rbl-default <pattern> (default=^127\.0\.0\.\d+$)
Matches <pattern> to rbl/rhsbl answers (regexp) if not specified in the ruleset.
--cacheid <item>, <item>, ...
This csv-separated list of request attributes will be used to construct
the request cache identifier. Use this only, if you know exactly what you
are doing. If you, for example, use postfwd only for RBL/RHSBL control,
you may set this to
postfwd --cache=3600 --cacheid=client_name,client_address
This increases efficiency of caching and improves postfwd’s performance.
Warning: You should list all items here, which are used in your ruleset!
--cleanup-requests <interval> (default=600)
The request cache will be searched for timed out items after this <interval> in
seconds. It is a minimum value. The cleanup process will only take place, when
a new request arrives.
--cleanup-rbls <interval> (default=600)
The rbl cache will be searched for timed out items after this <interval> in
seconds. It is a minimum value. The cleanup process will only take place, when
a new request arrives.
--cleanup-rates <interval> (default=600)
The rate cache will be searched for timed out items after this <interval> in
seconds. It is a minimum value. The cleanup process will only take place, when
a new request arrives.
-S, --summary <int> (default=600)
Shows some usage statistics (program uptime, request counter, matching rules)
every <int> seconds. This option is included by the -v switch.
This feature uses the alarm signal, so you can force postfwd to dump the stats
using ‘kill -ALRM <pid>‘ (where <pid> is the process id of postfwd).
Example:
Aug 19 12:39:45 mail1 postfwd[666]: [STATS] Counters: 213000 seconds uptime, 39 rules
Aug 19 12:39:45 mail1 postfwd[666]: [STATS] Requests: 71643 overall, 49 last interval, 62.88% cache hits
Aug 19 12:39:45 mail1 postfwd[666]: [STATS] Averages: 20.18 overall, 4.90 last interval, 557.30 top
Aug 19 12:39:45 mail1 postfwd[666]: [STATS] Contents: 44 cached requests, 239 cached dnsbl results
Aug 19 12:39:45 mail1 postfwd[666]: [STATS] Rule ID: R-001 matched: 2704 times
Aug 19 12:39:45 mail1 postfwd[666]: [STATS] Rule ID: R-002 matched: 9351 times
Aug 19 12:39:45 mail1 postfwd[666]: [STATS] Rule ID: R-003 matched: 3116 times
...
--no-rulestats
Disables per rule statistics. Keeps your log clean, if you do not use them.
This option has no effect without --summary or --verbose set.
-L, --stdoutlog
Redirects all syslog messages to stdout for debugging. Never use this with postfix!
-t, --test
In test mode postfwd always returns "dunno", but logs according
to it‘s ruleset. -v will be set automatically with this option.
-n, --nodns
Disables all DNS based checks like RBL checks. Rules containing
such elements will be ignored.
-n, --nodnslog
Disables logging of dns events.
--dns_timeout (default: 14)
Sets the timeout for asynchonous dns queries in seconds. This value will apply to
all dns items in a rule.
--dns_timeout_max (default: 10)
Sets the maximum timeout counter for dnsbl lookups. If the timeouts exceed this value
the corresponding dnsbl will be deactivated for a while (see --dns_timeout_interval).
--dns_timeout_interval (default=1200)
The dnsbl timeout counter will be cleaned after this interval in seconds. Use this
in conjunction with the --dns_timeout_max parameter.
--dns_async_txt
Perform dnsbl A and TXT lookups simultaneously (otherwise only for listings with at
least one A record). This needs more network bandwidth due to increased queries but
might increase throughput because the lookups can be parallelized.
--dns_max_ns_lookups (default=0)
maximum ns names to lookup up with sender_ns_addrs item. use 0 for no maximum.
--dns_max_mx_lookups (default=0)
maximum mx names to lookup up with sender_mx_addrs item. use 0 for no maximum.
-I, --instantcfg
The config files, specified by -f will be re-read for every request
postfwd receives. This enables on-the-fly configuration changes
without restarting. Though files will be read only if necessary
(which means their access times changed since last read) this might
significantly increase system load.
--config_timeout (default=3)
timeout in seconds to parse a single configuration line. if exceeded, the rule will
be skipped. this is used to prevent problems due to large files or loops.
Informational arguments
These arguments are for command line usage only. Never ever use them
with postfix spawn!
-C, --showconfig
Displays the current ruleset. Use -v for verbose output.
-P, --perfmon
This option turns of any syslogging and output. It is included
for performance testing.
-V, --version
Displays the program version.
-h, --help
Shows program usage.
-m, --manual
Displays the program manual.
REFRESH
In daemon mode postfwd reloads it’s ruleset after receiving a HUP
signal. Please see the description of the ’-I’ switch to have your
configuration refreshed for every request postfwd receives.
EXAMPLES
## whitelisting
# 1. networks 192.168.1.0/24, 192.168.2.4
# 2. client_names *.gmx.net and *.gmx.de
# 3. sender *@someshop.tld from 11.22.33.44
id=WL001; action=dunno ; client_address=192.168.1.0/24, 192.168.2.4
id=WL002; action=dunno ; client_name=\.gmx\.(net│de)$
id=WL003; action=dunno ; sender=@someshop\.tld$ ; client_address=11.22.33.44
## TLS control
# 1. *@authority.tld only with correct TLS fingerprint
# 2. *@secret.tld only with keysizes >=64
id=TL001; action=dunno ; sender=@authority\.tld$ ; ccert_fingerprint=AA:BB:CC..
id=TL002; action=REJECT wrong TLS fingerprint ; sender=@authority\.tld$
id=TL003; action=REJECT tls keylength < 64 ; sender=@secret\.tld$ ; encryption_keysize=64
## Combined RBL checks
# This will reject mail if
# 1. listed on ix.dnsbl.manitu.net
# 2. listed on zen.spamhaus.org (sbl and xbl, dns cache timeout 1200s instead of 3600s)
# 3. listed on min 2 of bl.spamcop.net, list.dsbl.org, dnsbl.sorbs.net
# 4. listed on bl.spamcop.net and one of rhsbl.ahbl.org, rhsbl.sorbs.net
id=RBL01 ; action=REJECT listed on ix.dnsbl.manitu.net ; rbl=ix.dnsbl.manitu.net
id=RBL02 ; action=REJECT listed on zen.spamhaus.org ; rbl=zen.spamhaus.org/127.0.0.[2-8]/1200
id=RBL03 ; action=REJECT listed on too many RBLs ; rblcount=2 ; rbl=bl.spamcop.net, list.dsbl.org, dnsbl.sorbs.net
id=RBL04 ; action=REJECT combined RBL+RHSBL check ; rbl=bl.spamcop.net ; rhsbl=rhsbl.ahbl.org, rhsbl.sorbs.net
## Message size (requires message_size_limit to be set to 30000000)
# 1. 30MB for systems in *.customer1.tld
# 2. 20MB for SASL user joejob
# 3. 10MB default
id=SZ001; state==END-OF-MESSAGE; action=REJECT message too large; size=30000000 ; client_name=\.customer1.tld$
id=SZ002; state==END-OF-MESSAGE; action=REJECT message too large; size=20000000 ; sasl_username==joejob
id=SZ003; state==END-OF-MESSAGE; action=REJECT message too large; size=10000000
## Selective Greylisting
# 1. if listed on zen.spamhaus.org with results 127.0.0.10 or .11, dns cache timeout 1200s
# 2. Client has no rDNS
# 3. Client comes from several dialin domains
id=GR001; action=greylisting ; rbl=dul.dnsbl.sorbs.net, zen.spamhaus.org/127.0.0.1[01]/1200
id=GR002; action=greylisting ; client_name=^unknown$
id=GR003; action=greylisting ; client_name=\.(t-ipconnect│alicedsl│ish)\.de$
## Date Time
date=24.12.2007-26.12.2007 ; action=450 4.7.1 office closed during christmas
time=04:00:00-05:00:00 ; action=450 4.7.1 maintenance ongoing, try again later
time=-07:00:00 ; sasl_username=jim ; action=450 4.7.1 to early for you, jim
time=22:00:00- ; sasl_username=jim ; action=450 4.7.1 to late now, jim
months=-Apr ; action=450 4.7.1 see you in may
days=!!Mon-Fri ; action=greylist
## Usage of jump
# The following allows a message size of 30MB for different
# users/clients while others will only have 10MB.
id=R001 ; action=jump(R100) ; sasl_username=^(Alice│Bob│Jane)$
id=R002 ; action=jump(R100) ; client_address=192.168.1.0/24
id=R003 ; action=jump(R100) ; ccert_fingerprint=AA:BB:CC:DD:...
id=R004 ; action=jump(R100) ; ccert_fingerprint=AF:BE:CD:DC:...
id=R005 ; action=jump(R100) ; ccert_fingerprint=DD:CC:BB:DD:...
id=R099 ; state==END-OF-MESSAGE; action=REJECT message too big (max. 10MB); size=10000000
id=R100 ; state==END-OF-MESSAGE; action=REJECT message too big (max. 30MB); size=30000000
## Usage of score
# The following rejects a mail, if the client
# - is listed on 1 RBL and 1 RHSBL
# - is listed in 1 RBL or 1 RHSBL and has no correct rDNS
# - other clients without correct rDNS will be greylist-checked
# - some whitelists are used to lower the score
id=S01 ; score=2.6 ; action=greylisting
id=S02 ; score=5.0 ; action=REJECT postfwd score too high
id=R00 ; action=score(-1.0) ; rbl=exemptions.ahbl.org,list.dnswl.org,query.bondedsender.org,spf.trusted-forwarder.org
id=R01 ; action=score(2.5) ; rbl=bl.spamcop.net, list.dsbl.org, dnsbl.sorbs.net
id=R02 ; action=score(2.5) ; rhsbl=rhsbl.ahbl.org, rhsbl.sorbs.net
id=N01 ; action=score(-0.2) ; client_name==$$helo_name
id=N02 ; action=score(2.7) ; client_name=^unknown$
...
## Usage of rate and size
# The following temporary rejects requests from "unknown" clients, if they
# 1. exceeded 30 requests per hour or
# 2. tried to send more than 1.5mb within 10 minutes
id=RATE01 ; client_name==unknown ; state==RCPT ; \
action==rate($$client_address/30/3600/450 4.7.1 sorry, max 30 requests per hour)
id=SIZE01 ; client_name==unknown ; state==END_OF_DATA ; \
action==size($$client_address/1572864/600/450 4.7.1 sorry, max 1.5mb per 10 minutes)
## Macros
# definition
&&RBLS { rbl=zen.spamhaus.org,list.dsbl.org,bl.spamcop.net,dnsbl.sorbs.net,ix.dnsbl.manitu.net; };
&&GONOW { action=REJECT your request caused our spam detection policy to reject this message. More info at http://www.domain.local; };
# rules
&&GONOW ; &&RBLS ; client_name=^unknown$
&&GONOW ; &&RBLS ; client_name=(\d+[\.-_]){4}
&&GONOW ; &&RBLS ; client_name=[\.-_](adsl│dynamic│ppp│)[\.-_]
## Groups
# definition
&&RBLS { \
rbl=zen.spamhaus.org ; \
rbl=list.dsbl.org ; \
rbl=bl.spamcop.net ; \
rbl=dnsbl.sorbs.net ; \
rbl=ix.dnsbl.manitu.net ; \
};
&&RHSBLS { \
...
};
&&DYNAMIC { \
client_name==unknown ; \
client_name~=(\d+[\.-_]){4} ; \
client_name~=[\.-_](adsl│dynamic│ppp│)[\.-_] ; \
...
};
&&BAD_HELO { \
helo_name==my.name.tld; \
helo_name~=^([^\.]+)$; \
helo_name~=\.(local│lan)$; \
...
};
&&MAINTENANCE { \
date=15.01.2007 ; \
date=15.04.2007 ; \
date=15.07.2007 ; \
date=15.10.2007 ; \
time=03:00:00 - 04:00:00 ; \
};
# rules
id=COMBINED ; &&RBLS ; &&DYNAMIC ; action=REJECT dynamic client and listed on RBL
id=MAINTENANCE ; &&MAINTENANCE ; action=DEFER maintenance time - please try again later
# now with the set() command, note that long item
# lists don’t have to be compared twice
id=RBL01 ; &&RBLS ; action=set(HIT_rbls=1)
id=HELO01 ; &&BAD_HELO ; action=set(HIT_helo=1)
id=DYNA01 ; &&DYNAMIC ; action=set(HIT_dyna=1)
id=REJECT01 ; HIT_rbls==1 ; HIT_helo==1 ; action=REJECT please see http://some.org/info?reject=01 for more info
id=REJECT02 ; HIT_rbls==1 ; HIT_dyna==1 ; action=REJECT please see http://some.org/info?reject=02 for more info
id=REJECT03 ; HIT_helo==1 ; HIT_dyna==1 ; action=REJECT please see http://some.org/info?reject=03 for more info
## combined with enhanced rbl features
#
id=RBL01 ; rhsblcount=all ; rblcount=all ; &&RBLS ; &&RHSBLS ; \
action=set(HIT_dnsbls=$$rhsblcount,HIT_dnsbls+=$$rblcount,HIT_dnstxt=$$dnsbltext)
id=RBL02 ; HIT_dnsbls>=2 ; action=554 5.7.1 blocked using $$HIT_dnsbls DNSBLs [INFO: $$HIT_dnstxt]
PARSER
Configuration
The postfwd ruleset can be specified at the commandline (-r option) or
be read from files (-f). The order of your arguments will be kept. You
should check the parser with the -C │ --showconfig switch at the
command line before applying a new config. The following call:
postfwd --showconfig \
-r "id=TEST; recipient_count=100; action=WARN mail with 100+ recipients" \
-f /etc/postfwd.cf \
-r "id=DEFAULT; action=dunno";
will produce the following output:
Rule 0: id->"TEST" action->"WARN mail with 100+ recipients"; recipient_count->"100"
...
... <content of /etc/postfwd.cf> ...
...
Rule <n>: id->"DEFAULT" action->"dunno"
Multiple items of the same type will be added to lists (see the "ITEMS"
section for more info):
postfwd --showconfig \
-r "client_address=192.168.1.0/24; client_address=172.16.26.32; action=dunno"
will result in:
Rule 0: id->"R-0"; action->"dunno"; client_address->"192.168.1.0/24, 172.16.26.32"
Macros are evaluated at configuration stage, which means that
postfwd --showconfig \
-r "&&RBLS { rbl=bl.spamcop.net; client_name=^unknown$; };" \
-r "id=RBL001; &&RBLS; action=REJECT listed on spamcop and bad rdns";
will result in:
Rule 0: id->"RBL001"; action->"REJECT listed on spamcop and bad rdns"; rbl->"bl.spamcop.net"; client_name->"^unknown$"
Request processing
When a policy delegation request arrives it will be compared against
postfwd‘s ruleset. To inspect the processing in detail you should
increase verbority using use the "-v" or "-vv" switch. "-L" redirects
log messages to stdout.
Keeping the order of the ruleset in general, items will be compared in
random order, which basically means that
id=R001; action=dunno; client_address=192.168.1.1; sender=bob@alice.local
equals to
id=R001; sender=bob@alice.local; client_address=192.168.1.1; action=dunno
Lists will be evaluated in the specified order. This allows to place
faster expressions at first:
postfwd -vv -L -r "id=RBL001; rbl=localrbl.local zen.spamhaus.org; action=REJECT" /some/where/request.sample
produces the following
[LOGS info]: compare rbl: "remotehost.remote.net[68.10.1.7]" -> "localrbl.local"
[LOGS info]: count1 rbl: "2" -> "0"
[LOGS info]: query rbl: localrbl.local 7.1.10.68 (7.1.10.68.localrbl.local)
[LOGS info]: count2 rbl: "2" -> "0"
[LOGS info]: match rbl: FALSE
[LOGS info]: compare rbl: "remotehost.remote.net[68.10.1.7]" -> "zen.spamhaus.org"
[LOGS info]: count1 rbl: "2" -> "0"
[LOGS info]: query rbl: zen.spamhaus.org 7.1.10.68 (7.1.10.68.zen.spamhaus.org)
[LOGS info]: count2 rbl: "2" -> "0"
[LOGS info]: match rbl: FALSE
[LOGS info]: Action: dunno
The negation operator !!(<value>) has the highest priority and
therefore will be evaluated first. Then variable substitutions are
performed:
postfwd -vv -L -r "id=TEST; action=REJECT; client_name=!!($$heloname)" /some/where/request.sample
will give
[LOGS info]: compare client_name: "unknown" -> "!!($$helo_name)"
[LOGS info]: negate client_name: "unknown" -> "$$helo_name"
[LOGS info]: substitute client_name: "unknown" -> "english-breakfast.cloud8.net"
[LOGS info]: match client_name: TRUE
[LOGS info]: Action: REJECT
Ruleset evaluation
A rule hits when all items (or at least one element of a list for each
item) have matched. As soon as one item (or all elements of a list)
fails to compare against the request attribute the parser will jump to
the next rule in the postfwd ruleset.
If a rule matches, there are two options:
* Rule returns postfix action (dunno, reject, ...) The parser stops
rule processing and returns the action to postfix. Other rules will not
be evaluated.
* Rule returns postfwd action (jump(), note(), ...) The parser
evaluates the given action and continues with the next rule (except for
the jump() or quit() actions - please see the "ACTIONS" section for
more information). Nothing will be sent to postfix.
If no rule has matched and the end of the ruleset is reached postfwd
will return dunno without logging anything unless in verbose mode. You
may simply place a last ‘catch-all´ rule to change that behaviour:
... <your rules> ...
id=DEFAULT ; action=dunno
will log any request that passes the ruleset without having hit a prior
rule.
INTEGRATION
Integration via daemon mode
The common way to use postfwd is to start it as daemon, listening at a
specified tcp port. As postfwd will run in a single instance
(multiplexing mode), it will take most benefit of it‘s internal caching
in that case. Start postfwd with the following parameters:
postfwd -d -f /etc/postfwd.cf -i 127.0.0.1 -p 10040 -u nobody -g nobody -S
For efficient caching you should check if you can use the options
--cache-rdomain-only, --cache-no-sender and --cache-no-size.
Now check your syslogs (default facility "mail") for a line like:
Aug 9 23:00:24 mail postfwd[5158]: postfwd n.nn ready for input
and use ‘netstat -an│grep 10040‘ to check for something like
tcp 0 0 127.0.0.1:10040 0.0.0.0:* LISTEN
If everything works, open your postfix main.cf and insert the following
127.0.0.1:10040_time_limit = 3600 <--- integration
smtpd_recipient_restrictions = permit_mynetworks <--- recommended
reject_unauth_destination <--- recommended
check_policy_service inet:127.0.0.1:10040 <--- integration
Reload your configuration with ‘postfix reload‘ and watch your logs. In
it works you should see lines like the following in your mail log:
Aug 9 23:01:24 mail postfwd[5158]: rule=22, id=ML_POSTFIX, client=english-breakfast.cloud9.net[168.100.1.7], sender=owner-postfix-users@postfix.tld, recipient=someone@domain.local, helo=english-breakfast.cloud9.net, proto=ESMTP, state=RCPT, action=dunno
If you want to check for size or rcpt_count items you must integrate
postfwd in smtp_data_restrictions or smtpd_end_of_data_restrictions. Of
course you can also specify a restriction class and use it in your
access tables. First create a file /etc/postfix/policy containing:
domain1.local postfwdcheck
domain2.local postfwdcheck
...
Then postmap that file (‘postmap hash:/etc/postfix/policy‘), open your
main.cf and enter
# Restriction Classes
smtpd_restriction_classes = postfwdcheck, <some more>... <--- integration
postfwdcheck = check_policy_service inet:127.0.0.1:10040 <--- integration
127.0.0.1:10040_time_limit = 3600 <--- integration
smtpd_recipient_restrictions = permit_mynetworks, <--- recommended
reject_unauth_destination, <--- recommended
... <--- optional
check_recipient_access hash:/etc/postfix/policy, <--- integration
... <--- optional
Reload postfix and watch your logs.
Integration via xinetd
There might be several reasons for you to use postfwd via a tcp wrapper
package like xinetd (see <http://www.xinetd.org/>). I won‘t discuss
that here. If you plan to do so, just add the following line to your
/etc/services file:
# postfwd port
postfwd 10040/tcp
Then create a file ’/etc/xinetd.d/postfwd’:
{
interface = 127.0.0.1
socket_type = stream
protocol = tcp
wait = no
user = nobody
server = /usr/local/bin/postfwd
server_args = -f /etc/postfwd.cf
disable = no
}
and restart the xinetd daemon (usually a SIGHUP should be fine). If you
experience problems you might want to check your system’s log for
xinetd errors like "socket already in use".
The integration with postfix is similar to the Integration via daemon
mode section above. Reload postfix and watch your logs to see if
everything works.
TESTING
First you have to create a ruleset (see Configuration section). Check
it with
postfwd -f /etc/postfwd.cf -C
There is an example policy request distributed with postfwd, called
’request.sample’. Simply change it to meet your requirements and use
postfwd -f /etc/postfwd.cf <request.sample
You should get an answer like
action=<whateveryouconfigured>
For network tests I use netcat:
nc 127.0.0.1 10040 <request.sample
to send a request to postfwd. If you receive nothing, make sure that
postfwd is running and listening on the specified network settings.
PERFORMANCE
Some of these proposals might not match your environment. Please check
your requirements and test new options carefully!
- use caching options
- use the correct match operator ==, <=, >=
- use ^ and/or $ in regular expressions
- use item lists (faster than single rules)
- use set() action on repeated item lists
- use jumps and rate limits
- use a pre-lookup rule for rbl/rhsbls with empty note() action
SEE ALSO
See <http://www.postfix.org/SMTPD_POLICY_README.html> for a description
of how Postfix policy servers work.
LICENSE
postfwd is free software and released under BSD license, which
basically means that you can do what you want as long as you keep the
copyright notice:
Copyright (c) 2007, Jan Peter Kessler All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
* Neither the name of the authors nor the names of his contributors
may be used to endorse or promote products derived from this
software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY ME ‘‘AS IS’’ AND ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN
NO EVENT SHALL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
AUTHOR
Jan Peter Kessler <info (AT) postfwd (DOT) org>. Let me know, if you
have any suggestions.