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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.

       There is no provision to support IPv6-based lists, because none yet
       exist. IPv6-based access list support will be added in the future.

       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 IP address

       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, or to
       “Access denied.”	 if the DNS access list did not return a TXT record.
       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 any TXT
       record in the DNS access list. Note that this is a single parameter to
       couriertcpd, so the parameter must be quoted if it contains any spaces
       or special shell metacharacters.

       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		  06/27/2015			COURIERTCPD(1)

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