Using HACK(relaycontrol) in your .mc file

This is a brief summary of the customization options used with
HACK(relaycontrol).  For more general information on what this
does and how it works see:

http://hexadecimal.uoregon.edu/antirelay/

Default values are shown for optional items in the examples
below.

define(`confRELAYS', `')

   Optional.  Define the initial contents of class R in
   sendmail.cf.  Class R lists hosts or domain names (see
   HACK(r_domains) below) that you will relay mail to, and
   maybe also hosts or domains you will permit unlimited
   relaying from (see HACK(r_clients) below).

define(`confCR_FILE', `-o /usr/local/etc/sendmail.cR')

   Optional.  Specify the location of the file that
   defines/extends class R.

define(`RELAY_TO_DOMAIN',   `hash -o /usr/local/etc/relay_to_domain')
define(`RELAY_TO_IP',       `hash -o /usr/local/etc/relay_to_ip')
define(`RELAY_FROM_DOMAIN', `hash -o /usr/local/etc/relay_from_domain')
define(`RELAY_FROM_IP',     `hash -o /usr/local/etc/relay_from_ip')

   Optional.  Specify types and locations of the relay permission
   databases.

define(`RELAY_ERROR', `5.5.1')
define(`RELAY_MESSAGE', `"551 Relaying denied"')

   Optional.  Use to specify the SMTP error code and
   error message output when relaying is denied.

HACK(use_cr_file)

   Optional.  Read a file to define/extend class R.

HACK(r_domains)

   Optional.  If included, items in class R will match any host
   in a domain rather than strictly matching host names (i.e. if
   "domain.com" is in class R and HACK(rdomains) is used, then
   "domain.com" will match "domain.com", "host.domain.com",
   etc.).

HACK(r_clients)

   Optional.  If included, client host or domain names will be
   checked against class R and allowed to relay if they match.
   Otherwise class R specifies only who you will relay TO, not
   who you permit relaying FROM.

HACK(class_a_relay)

   Optional.  If included, single-octet class A IP addresses will
   be matched on the left when checking relay permissions
   (i.e. 24 will match 24.*.*.*).  Otherwise IP addresses must be
   specified and matched with at least two octets on the left
   (i.e. 128.223.*.*).

HACK(relaycontrol)

   Defines check_rcpt ruleset and its dependent local
   configuration options, customized using the above
   defines/HACKs.