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COURIERTCPD(1)		    Double Precision, Inc.		COURIERTCPD(1)

       couriertcpd - the Courier mail server TCP server	daemon

       couriertcpd [-pid=pidfile] [option...] {list} {program} {arg...}

       couriertcpd {-pid=pidfile} {-stop}

       couriertcpd {-pid=pidfile} {-restart}

       couriertcpd accepts incoming network connections, and runs program
       after establishing each network connection. The program's standard
       input and output	are set	to the network connection.

       list is a comma-separated list of TCP port numbers where	incoming
       connections are created.	 program is the	program	to run.	If program
       requires	any arguments, they are	specified on the command line, after
       program itself.

       Before running program, couriertcpd initializes several environment
       variables that describe the network connection. The environment
       inherited by program will be the	environment inherited by couriertcpd,
       plus any	additional environment variables initialized by	couriertcpd.
       It is also possible to reject certain network connections. Several
       options are available to	specify	which network connections will be

	   Specifies an	optional access	file. The access file lists the	IP
	   addresses from which	connections should be accepted or rejected.
	   The access file is also used	to initialize environment variables
	   based on the	IP address of the connection.  filename	is a GDBM or
	   DB database file that's usually created by a	script from one	or
	   more	text files. See	"ACCESS	FILE" below for	more information.

	   Lookup the local interface IP and port in the access	file, in
	   addition to looking up the remote IP. This gives a mechanism	for
	   setting environment variables depending on which IP address and/or
	   port	the client connected to. In the	access file, ""
	   matches connections to IP address port 25; ""
	   matches connections to IP address on	any port; and "*.25"
	   matches connections to port 25 on any IP address.

	   Accept network connections only to IP address n.n.n.n. If not
	   specified, couriertcpd accepts connections to any IP	address	that
	   the system accepts connections on. If the system has	multiple
	   network interfaces with separate IP addresses, this option makes
	   couriertcpd accept connections only to one specific IP address.
	   Most	systems	have multiple network interfaces: the loopback
	   interface, plus the local network interface,	so that
	   -address= accepts connections only from the	local system.
	   When	multiple port numbers are specified, it	is also	possible to
	   selectively bind different network addresses	to each	port number
	   when	list specifies more than one port number. See "Multiple	port
	   list[1]" below for more information.

       -block=zone[,var[/n.n.n.n][,msg]] or -allow=zone[,var[/n.n.n.n[,]]]
	   Initialize the environment variable var if both of the following
	   conditions are true:	var is not already initialized;	the connecting
	   IP address can be found in a	DNS-based access list. See DNS ACCESS
	   LISTS, below. Multiple -block and -allow options can	be specified.

	   -block and -allow are very similar, differing only in minor
	   semantics.  -block's	semantics are more appropriate for using DNS
	   access list to block	access,	and -allow's semantics are more
	   appropriate for using DNS access list to whitelist IP addresses and
	   exempt them even if they appear in other -blocked zones.

	   Specifies an	optional message to be returned	to the client if the
	   -access option rejects them.	The default is to drop the TCP
	   connection without sending back any messages.

	   If the environment variable var is set to a nonempty	value,
	   terminate immediately. Do not run the program to handle the
	   connection. See DNS ACCESS LISTS, below, for	more information.  var
	   defaults to "BLOCK",	if not specified.

	   Set couriertcpd's its group ID.  group may be specified
	   numerically,	or by its name.	Only the superuser may use -group.

	   Length of the queue which holds pending connections.	 n is a
	   number. If not specified, the system	default	is used.

	   Maximum number of connections accepted from the same	C network
	   block. Using	this option is recommended, because connection slots
	   are limited.	Without	this option, the same C	network	block can
	   potentially use up all available connection slots.

	   Maximum number of connections accepted from the same	IP address.
	   Use both the	-maxperc and -maxperip options to fine tune connection
	   limits. For example,	when couriertcpd is listening on the SMTP port
	   it makes sense to set an upper limit	on the number of connections
	   from	the same C block. Domains that send a large amount of mail
	   often have multiple servers sending outbound	mail from the same C
	   block, so it	makes sense to set limits on individual	C blocks. On
	   the other hand, if couriertcpd is listening on the POP3 port	it
	   makes more sense to set limits on individual	IP addresses. If a C
	   block of addresses is assigned to a dialup modem pool, it is
	   certainly possible to have many IP addresses	within the same	C
	   block have connections to the POP3 server at	the same time.

	   The -maxperip option	can be overridden for a	given IP address by
	   setting the MAXCPERIP environment variable, see "Setting
	   environment variables" for more information.

	   Maximum number of connection	slots, or the maximum number of
	   processes started. This effectively specifies the maximum number of
	   connections accepted	at the same time. After	the maximum number of
	   connections has been	opened,	couriertcpd waits for an existing
	   connection to close,	before accepting any more connections.

	   Log a LOG_WARNING message to	syslog when the	number of active
	   processes exceeds n.	The default is 90% of maxprocs.	 couriertcpd
	   logs	a LOG_ALERT syslog message when	the number of active processes
	   reaches the maximum.

	   Do not look up the hostname associated with connecting IP address
	   and the local addres, do not	initialize the TCPREMOTEHOST or
	   TCPLOCALHOST	environment variables (see below).

	   Do not perform an ident lookup, and do not initialize the
	   TCPREMOTEINFO environment variable.

	   If given, couriertcpd puts itself into the background and saves its
	   process ID in this file, usually somewhere in /var/run.

	   This	option must also be present when using the -restart and	-stop

	   Send	a SIGHUP to an existing	couriertcpd process. Specify the same
	   -pid	argument as the	one that was used to start couriertcpd.	The
	   process ID is read from the -pid file, and the couriertcpd receives
	   a SIGHUP signal.

	   Set program's standard error	to the network connection, just	like
	   its standard	input and output.

	   Set program's standard error	to the specified file, logfile.	The
	   file	is created, if necessary, and is opened	in append mode.

	   Set program's standard error	to a pipe, which is read by
	   logprogram. Only one	instance of logger is started, which receives
	   standard error from every instance of program. The specified	logger
	   is executed with the	output end of the stderr pipe connected	as
	   standard input.  logprogram is executed with	one argument -
	   program's name.

	   Use name as the argument to logprogram, instead of the program's

	   Stop	(kill) an existing couriertcpd process.	Specify	the same -pid
	   argument as the one that was	used to	start couriertcpd. The process
	   ID is read from the -pid file, and the couriertcpd process is
	   killed. All child processes of couriertcpd will receive a SIGTERM

	   Set couriertcpd's user ID. Also, the	group ID is set	to the user's
	   group ID. Using both	-group and -user is not	necessary. Only	the
	   superuser can specify -user.

       The list	argument can be	a comma-separated list of multiple port
       numbers.	 couriertcpd will create network connections on	any listed
       port. Each port number can be optionally	specified as "address.port",
       for example:

	   couriertcpd -pid=/var/run/,999 program

       This instance accepts network connections to either port	25 or port
       999, however connections	on port	25 are created only on the IP address, the loopback interface.

       Whenever	an IP address is not specified,	network	connections are
       accepted	to any IP address (called "wildcarding"). On IPv6-capable
       systems,	couriertcpd will attempt to create two incoming	network
       connection ports, if an IP address is not specified. After creating the
       first port as an	IPv6 wildcard port, couriertcpd	will then attept to
       create an IPv4 wildcard port, with the same port	number.	Some
       BSD-derived systems must	use separate IPv6 and IPv4 wildcard ports to
       create incoming network connections. Most other systems only need an
       IPv6 port to create both	IPv6 and IPv4 incoming network connections.
       couriertcpd quietly ignores a failure to	create an IPv4 wildcard	port,
       as long as an IPv6 wildcard was succesfully created.

       The -address option can be used to default a specific IP	address	for
       every listed port number. For example:

	   couriertcpd -pid=/var/run/, program


	   couriertcpd -pid=/var/run/ -address= 25,999	program

       will create network connections on ports	25 and 999 of the IP address

       The access file lists IP	addresses that couriertcpd will	accept or
       reject connections from.	An access file is optional. Without an access
       file couriertcpd	accepts	a connection from any IP address.

       Both IPv4 and IPv6 addresses can	be specified, if IPv6 support is
       available. A non-standard syntax	is currently used to specify IPv6
       addresses. This is subject to change in the near	future.	IPv6 support
       is currently considered to be experimental.

       The access file is a binary database file that's	usually	created	by a
       script, such as makesmtpaccess(8)[2], or	makeimapaccess(8)[3], from one
       or more plain text files. Blank lines in	the text file are ignored.
       Lines that start	with the # character are also ignored.

   Rejecting and accepting connections by IP address
       The following line instructs couriertcpd	to reject all connections from
       an IP address range:


       netblock	is an IP address, such as  <tab> is	the ASCII tab
       character. There	MUST be	exactly	one tab	character after	the IP address
       and the word "deny".

       You can also block connections from an entire network C block:


       This blocks connections from IP addresses through Blocking connections from an entire B or A	network	block
       works the same way.

       Use the word "allow" instead of "deny" to explicitly allow connections
       from that IP address or netblock. For example:


       This blocks all connections from to except for These two lines can	occur in any order.  couriertcpd
       always uses the line with the most specific IP address.

       If the IP address of the	connection is not found	in the access file the
       connection is accepted by default. The following	line causes unlisted
       connections to be rejected:


   IPv6	addresses
	   IPv6	support	in the access file is experimental, and	is subject to
	   change in a future release. The following syntax is subject to
	   change at any time.

       The access file can also	specify	IPv6 addresses,	if IPv6	support	is
       available. The existing IPv4 address format is used for IPv6-mapped
       IPv4 addresses, and no changes are required. For	all other IPv6
       addresses use the following format:


       The IPv6	address	must begin with	:. The initial : character is not
       really a	part of	the IPv6 address, it is	only used to designate this
       record as an IPv6 address, allowing an access file to contain a mixture
       of IPv4 and IPv6	addresses. The IPv6 address follows the	initial	:
       character, and it must be spelled out using zero-padded lowercase
       hexadecimal digits. For example:


       Netblocks must be specified using even-word boundaries only:


       This will deny entire 3ffe::/16 (6bone network, which is	phased out).


       This will deny 2002:c0a8::/32 (6to4 addresses derived from private
       address space).

   Setting environment variables
       allow can be optionally followed	by a list of environment variable
       assignments, separated by commas. The environment variables are set
       before executing	program	or checking access lists (see below). For


       This sets RELAYCLIENT environment variable for connections from the
       192.68.0	block. In addition to that, the	SIZELIMIT environment variable
       is set to 1000000 if the	connection comes from the IP address

       Note that RELAYCLIENT must be explicitly	specified for the IP address The	first line is NOT used for connections from this IP
       address.	 couriertcpd only reads	one entry from the access file,	the
       entry for the most specific IP address.<tab>allow,MAXCPERIP=100

       couriertcpd itself implements the MAXCPERIP environment variable
       setting in the access file, as an override to the -maxperip parameter,
       which specifies the maximum number of connections from the same IP
       address.	If specified in	the access file	for an IP address, or an IP
       address range, the value	given by MAXCPERIP overrides it.

       An alternative to listing banned	IP addresses in	access files is	to use
       an external DNS-based IP	access list.

       couriertcpd's default configuration does	not automatically reject
       connections from	banned IP address unless the -drop option is present.
       Instead,	couriertcpd sets an environment	variable if the	connecting
       address has a hit in the	DNS access list. The Courier mail server
       rejects all mail	if the connection's environment	has the	environment
       variable	BLOCK set to a non-empty string, and it	just so	happens	that
       -block and -allow set the BLOCK environment variable by default.

       -allow and -block's parameter gives the DNS zone	where the access list
       query gets performed. In	this example, couriertcpd makes	a DNS query
       for "",	then, if necessary, for
       "", for	a connection from the IPv4 address

       For IPv6	addresses, the DNS query consists of individual	hexadecimal
       nybbles (in reverse order, like the IPv4	query).

       If the DNS query	succeeds (more details below), -allow sets the
       environment variable to an empty	string,	and -block sets	the
       environment variable from the TXT record	in the DNS response, if	one
       was requested (see below), or to	a default message for regular DNS
       queries for A records. It should	be possible to use couriertcpd with
       DNS access lists	that use either	A or TXT records.

       The DNS zone parameter to -allow	and -block has up to three additional
       components, which must be given in the following	order, if more than
       one optional component gets specified:,BLOCK2

       The environment variable	that gets set by the DNS access	list query can
       be changed from the default of BLOCK to something else, BLOCK2 in this
       example.	The Courier mail server	pays attention only to BLOCK, this is
       for the benefit of local	or custom hacks, which want to leverage
       couriertcpd's DNS access	list lookup facilities,	but want it for	other

       couriertcpd's DNS access	list lookup normally ignores the contents of
       the actual A record in the DNS access list, however some	DNS access
       lists may use different A record	to indicate different kinds of
       records.	Given an explicit IP address to	couriertcpd results in the
       environment variable getting set	only if	the lookup returned the
       matching	A record. An A record must exist in the	DNS access list, in
       addition	to any TXT record. If an explicit IP address is	not given, any
       A or TXT	record sets -allow and -block's	environment variable.,BLOCK,Go away

       The last	component specifies a custom message that overrides the
       default rejection message. Note that this is a single parameter to
       couriertcpd, so the parameter must be quoted if it contains any spaces
       or special shell	metacharacters.	A message that's specified as "*"
       results in a TXT	query to the DNS access	list instead of	the regular A
       query. This is for DNS access lists that	provide	TXT records, that gets
       copied into the BLOCK variable (or the custom variable).	The "*"	must
       also be quoted, since it's also a shell metacharacter, and it cannot be
       used together with an explicit A	address	query, described above.

       The custom message parameter gets specified for the -block, option.
       -allow also allows takes	this parameter,	but it has a different
       meaning.	If its set, even if it's an empty string, couriertcpd looks
       for TXT records in the DNS access list that's used as a whitelist, in
       addition	to the A records (using	the "any" query):,BLOCK,

       Without this parameter couriertcpd queries for A	records	only.

       Finally,	a literal IP address, if given,	must always follow the
       variable	name:,BLOCK/,Go away

       -block normally searches	the DNS	access list for	either A or TXT
       records using the "any" DNS query. Sometimes this can cause problems,
       or not work at all, with	older DNS servers. Specifying a	custom message
       results in -block executing an ordinary A DNS query.  -allow always
       uses an A query.

       Multiple	-block and -allow options can be given.	The connecting IP
       address gets looked up in multiple access lists.	This is	implemented as

       couriertcpd processes all -block	and -allow options in list order. If
       each option's environment variable (BLOCK or something else) is already
       set, couriertcpd	skips the DNS access list lookup. Therefore, when
       multiple	options	use the	same environment variable, the first DNS
       access list it exists in	will set the environment variable, and the
       remaining ones get ignored, but any remaining -blocks and -allows for
       different environment variables still get processed.

       It follows that,	in general, -allow options should always be listed
       first, before any -blocks; but it's also	possible to implement a
       complicated policy with some -allows, then some -blocks,	then more
       -allows and -blocks.

       Three additional	environment variables may get set in conjunction with
       a successful DNS	access list lookup:


	   The contents	of the A record	in the DNS access list,	if one exists
	   (this is not	set for	DNS access lists that use TXT record).


	   The contents	of the TXT record in the DNS access list, if one
	   exists. This	will generally be the same as BLOCK for	-blocks, but
	   will	also provide the contents of the TXT record for	-allows	(if it
	   has a dummy custom message portion) which always set	BLOCK to an
	   empty string.


	   The DNS zone	of the succesfull access list lookup, like

       -block and -allow options that specify a	custom environment variable
       name follow the same naming convention, of appending "_IP", "_TXT", and
       "_ZONE" suffix to the name of the custom	environment variable.

       Including "allowok" keyword in an SPF setting automatically passes the
       SPF check for senders whose IP address is found in an -allow-ed access
       list. See courier(8)[4].

       couriertcpd also	initializes the	following environment variables	prior
       to running program:

	   The name of the host	on the local end of the	network	connection,
	   looked up in	DNS.  TCPLOCALHOST will	not be set if the IP address
	   of the network connection's local end cannot	be found in DNS, or if
	   -nodnslookup	option is specified.  TCPLOCALHOST will	be set to the
	   string softdnserr if	the DNS	lookup fails with a temporary error
	   (so you cannot tell if the IP address has a valid host name
	   associated with it),	or if the reverse and forward DNS lookups do
	   not match.  TCPLOCALHOST will not be	set if the reverse DNS lookup
	   fails completely.

	   The IP address of the local end of the network connection.

	   Rhe number of the port of the local end of the network connection.

	   The hostname	of the connecting host.	Like TCPLOCALHOST, but for the
	   connecting IP address.

	   Connecting IP address.

	   Identification string received from the IDENT server	on the remote
	   IP address. Not set if the IDENT server returned an error, or if
	   the -noidentlookup option was specified.

	   TCP port of the remote end of the network connection.


       Sam Varshavchik

	1. Multiple port list
	   [set	$man.base.url.for.relative.links]/#list

	2. makesmtpaccess(8)
	   [set	$man.base.url.for.relative.links]/makesmtpaccess.html

	3. makeimapaccess(8)
	   [set	$man.base.url.for.relative.links]/makeimapaccess.html

	4. courier(8)
	   [set	$man.base.url.for.relative.links]/courier.html

Courier	Mail Server		  03/11/2017			COURIERTCPD(1)


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