option=value

[SERVICE=service-name]

BACKLOG=integer

Controls the depth of the TCP backlog queue for the socket. The default value for each service is MAX_CONNS*MAX_PROCS (with a minimum value of 5). This option should not be set higher than the underlying TCP/IP kernel supports.

DEBUG

Enables debugging output. Enabling all debugging is done by setting the option to -1. The actual meaning of each bit is described in Table 4–27.

DNS_VERIFY_DOMAIN

Specifies the host name or IP address of source against which to check incoming connections. Various groups maintain information about unsolicited email sources or open relay sites. Some sites check incoming IP connections against the lists maintained by such groups. Up to five DNS_VERIFY_DOMAIN options can be specified for each service. Note that SMTP is typically the only service for which such checks make sense. For example:

[SERVICE=SMTP]

PORT=25

DNS_VERIFY_DOMAIN=rbl.maps.siroe.com

DNS_VERIFY_DOMAIN=dul.maps.siroe.com

If this options is enabled on a well known port (25, 110, or 143), then a standard message such as the one below is sent before the connection is closed: 

500 5.7.1 access_control: host 192.168.51.32 found on DNS list and rejected

If you wish the MTA to log such rejections, the 24th bit of the Dispatcher debugging DEBUG option can be set (DEBUG=16%1000000) to cause logging of the rejections to the dispatcher.log file. Log entries take the following form:

access_control: host a.b.c.d found on DNS list and rejected

ENABLE_RBL=0 or 1

This option is deprecated. You should use the DNS_VERIFY_DOMAIN option or the dns_verify callout from the PORT_ACCESS mapping table instead.

HISTORICAL_TIME=integer

Controls how long the expired connections (those that have been closed) and processes (those that have exited) remain listed for statistical purpose in the Dispatcher statistics. 

INTERFACE_ADDRESS=IP address

The INTERFACE_ADDRESS option can be used to specify the IP address interface to which the Dispatcher service should bind. By default, the Dispatcher binds to all IP addresses. But for systems having multiple network interfaces each with its own IP address, it may be useful to bind different services to the different interfaces. Note that if INTERFACE_ADDRESS is specified for a service, then that is the only interface IP address to which that Dispatcher service bind. Only one such explicit interface IP address may be specified for a particular service (though other similar Dispatcher services may be defined for other interface IP addresses).

IDENT=0 or 1

If IDENT=1 is set for a service, it causes the Dispatcher to try an IDENT query on incoming connections for that service, and to note the remote username (if available) as part of the Dispatcher statistics. The default is IDENT=0, meaning that no such query is made.

IMAGE=file specification

Specifies the image that is run by server processes when created by the Dispatcher. The specified image should be one designed to be controlled by the Dispatcher. 

LOGFILE=file specification

Causes the Dispatcher to direct output for corresponding server processes to the specified file. LOGFILE can include a %s which includes the local system’s hostname in the file specification. For example, LOGFILE=tcp_smtp_server_%s.log on node freddy results in log files with the name tcp_smtp_server_freddy.log-*.

MAX_CONNS=integer

Specifies a maximum number of connections that may be active on any server process. The MAX_CONNS option affects the Dispatcher’s management of connections. The default value for MAX_CONNS is 10. The maximum possible value for MAX_CONNS is 50.

The choice of setting this option is mainly a performance issue relating to the number of processes and the size of the process virtual address space. 

Setting MAX_CONNS to higher values allows more connections, but at the potential cost of decreased performance for each individual connection. If it is set to 1, then for every incoming client connection, only one server process is used. Note that the value of MAX_CONNS multiplied by the value of MAX_PROCS controls the maximum number of simultaneous connections that can be accepted.

MAX_HANDOFFS=integer

Specifies the maximum number of concurrent asynchronous hand-offs in progress that the Dispatcher allows for newly established TCP/IP connections to a service port. The default value is 5.

MAX_IDLE_TIME=integer

Specifies the maximum idle time for a server process. When an server process has had no active connections for this period, it becomes eligible for shutdown. This option is only effective if there are more than the value of MIN_PROCS server processes currently in the Dispatcher’s pool for this service.

MAX_LIFE_CONNS

Specifies the maximum number of connections an server process can handle in its lifetime. Its purpose is to perform worker-process housekeeping. 

MAX_LIFE_TIME=integer

Requests that server processes be kept only for the specified number of seconds. This is part of the Dispatcher’s ability to perform worker-process housekeeping. When an server process is created, a countdown timer is set to the specified number of seconds. When the countdown time has expired, the SMTP server process is subject to shutdown. Default value is 86400 (one day).

MAX_PROCS=integer

Controls the maximum number of server processes that are created for this service. 

MAX_SHUTDOWN=integer

Specifies the maximum number of server processes which can be in the shutdown state. In order to provide a minimum availability for the service, the Dispatcher does not shut down server processes that might otherwise be eligible for shutdown if shutting them down results in having more than MAX_SHUTDOWN server processes for the service in the shutdown statue. This means that processes that are eligible for shutdown can continue running until a shutdown “slot” is available.

MIN_CONNS=integer

Determines the minimum number of connections that each Worker Process must have before considering the addition of a new server process to the pool of currently available server processes. The Dispatcher attempts to distribute connections evenly across this pool. 

MIN_PROCS=integer

Determines the minimum number of server processes that are created by the Dispatcher for the current service. Upon initialization, the Dispatcher creates this many detached processes to start its pool. When a process is shut down, the Dispatcher ensures that there are at least this many available processes in the pool for this service. 

PARAMETER

The interpretation and allowed values for the PARAMETER option are service specific. In the case of an SMTP service, the PARAMETER option may be set to CHANNEL=channelname, to associate a default TCP/IP channel with the port for that service. For instance:

[SERVICE=SMTP_SUBMIT]

PORT=587

...

PARAMETER=CHANNEL=tcp_incoming

This can be useful if you want to run servers on multiple ports—if your internal POP and IMAP clients have been configured to use a port other than the normal port 25 for message submission, separating their message traffic from incoming SMTP messages from external hosts—and if you want to associate different TCP/IP channels with the different port numbers. 

PORT=integer...

Specifies the TCP port(s) to which the Dispatcher listens for incoming connections for the current service. Connections made to this port are transferred to one of the SMTP server processes created for this service. Specifying PORT=0 disables the current service.

STACKSIZE

Specifies the thread stack size of the server. The purpose of this option is to reduce the chances of the server running out of stack when processing deeply nested MIME messages (several hundreds of levels of nesting). Note that these messages are in all likelihood spam messages destined to break mail handlers. Having the server fail protects other mail handlers farther down the road.