19970615/mea

	SPAM is an increasing problem, and one aspect of it is
	unauthorized email relaying thru various smtp servers.


	Our initial mechanisms work well for systems that are not
	used for outbound relaying, but may be acting as inbound
	MX backup relays.

	Even the outbound relays are supported, but the sender
	domain/address validities are not currently verifiable.


	For the in-depth document of the mechanism, see file
		$MAILVAR/db/smtp-policy.src
	and for a sample policy builder script, see file
		$MAILBIN/policy-builder.sh
	from which starting comments following text is taken:

# Sample smtp-policy-db builder script.
#
# This merges following files from $MAILVAR/db/ directory:
#	smtp-policy.src
#	localnames	  ('= _full_rights')
#	smtp-policy.relay ('= _full_rights')
#	smtp-policy.mx	  ('relaytargets +')
#	smtp-policy.spam  ('= _bulk_mail')
#
# These all together are used to produce file:  smtp-policy.$DBEXT
# The produced database retains the first instance of any given key.


	The currect builder script, and basic smtp-policy.src file
	together accept email to all of our local addresses, and
	will allow any destination addresses as long as HELO/EHLO
	and/or MAIL FROM:<..> addresses are either one of our localnames,
	or listed as hosts, or domain suffixes at smtp-policy.relay,
	and/or smtp-policy.mx -files.

	If the MAIL FROM:<..> address, or its domain can be found from
	file  smtp-policy.spam,  then the message is rejected.


		-----------------------------------

	Alternate behavioral models can be built; for some ideas
	see	http://www.sendmail.org/antispam.html
	and	http://spam.abuse.net/spam/tools/mailblock.html
