divert(-1)

dnl ###################################################################
dnl #	This crudel checks for the validity of the "From:" header and
dnl #	the "Message-Id:" header, and rejects mail where the headers
dnl #	are obviously invalid.
dnl #
dnl #	For the "From:" header, anything of the form *@* is accepted,
dnl #	where the "*" wildcards match non-empty strings.
dnl #
dnl #	An unqualified address, or a missing "From:" header is also
dnl #	allowed, if the envelope sender address contains an "@".  The
dnl #	principle is that sendmail can generate a valid "From:" in
dnl #	this case, perhaps depending on the "C" mailer flag for smtp
dnl #	mailers.  However, when the envelope sender is null (<>), as
dnl #	with some spam, stricter standards for "From:" are required.
dnl #
dnl #	The "Message-Id:" header, if it exists, is required to be of
dnl #	the form: comment <id@hostname> comment.  There is no check
dnl #	of an absent header in this case, since the standards do not
dnl #	require the header.
dnl #
dnl #	There is a check for access map entries for host or ip
dnl #	address, tagged with "CheckMsgid".  This allows a particular
dnl #	sending host to be whitelisted, bypassing message-id
dnl #	rejections for that host.  The entry for a host can be OK or
dnl #	RELAY, which whitelist the host.  It can also be DISCARD to
dnl #	silently discard bad message-id mail from this host.
dnl #
dnl #	I probably should add a similar "CheckFrom:" tagging, but
dnl #	I have not yet found any need for that.
dnl #
dnl ###################################################################
dnl #
dnl #	The macro ${HeadersSeen} is used to keep track, for checking
dnl #	in an end of header check.  It is expected to contain a
dnl #	string of key letters, one for each header whose presence is
dnl #	recorded.  At present it is used only for "F" for the "From:"
dnl #	header, and "M" for the "Message-Id:" header.

divert(0)dnl
VERSIONID(`$Id: reject_bad_from.m4,v 1.2 2001/10/18 00:58:20 rickert Exp $')
divert(-1)

define(`_NEED_MACRO_MAP_')dnl
LOCAL_CONFIG
HFrom: $>CheckFrom
HMessage-Id: $>CheckMsgid
LOCAL_RULESETS
SCheckFrom
## First record that we have seen this header.
R$*		$:$(macro {HeadersSeen} $@ $&{HeadersSeen} F $) $1
R$+ @ $+	$@ ok		Passes crude check
R$*		$: $&f		Recover envelope sender.
R$+ @ $+	$@ ok		With C mailer flag, will use sender @domain
R$*		$#error $: "553 Bogus 'From:' header"

SCheckMsgid
## First record that we have seen this header.
R$*		$:$(macro {HeadersSeen} $@ $&{HeadersSeen} M $) $1
R$*<$+@$+>$*	$@ ok		Passes crude check
R$*		$:<$&{client_addr}><$&{client_name}>	Client addr/name
R<$+><$+>	$: $>A <$1> <?> <! CheckMsgid> <$2>
R<?><$+>	$: $>D <$1> <?> <! CheckMsgid> <>
R<?>$*		$: <$(access CheckMsgid: $: ? $)>	Default
R<$={Accept}>$*	$@ ok
R<DISCARD>$*	$#discard $: discard
R$*		$#error $: "553 Bogus \"Message-Id:\" header"

Scheck_eoh
R$*		$:<$&f>$&{HeadersSeen}	recover list of seen headers
R$*		$:$(macro {HeadersSeen} $@ $) $1	and reset list
R<$*>$* F $*	$@ ok			"From:" seen.
R<> $*		$#error $: "553 Missing 'From:' header"
#R<$+>$*	$@ ok			sendmail will generate from envelope