>Sorry for the wide distribution,
>
>Is there any way in sendmail to disallow incoming mail from a place
>whose IP address does not map to a FQDN?

off the top of my head, something like this might do what you want...

LOCAL_RULESETS
SLocal_check_rcpt
R$*			$: <$&{client_resolve}> <$&{client_name}>
R<TEMP> <$*>		$@ Basic_check_rcpt_will_decide
R<FORGED> <$*>		$@ Basic_check_rcpt_will_decide
R<FAIL> <$*>		$@ Basic_check_rcpt_will_decide
R<$*> <$*.>		$1
R<$*> <$*.$*>		$@ OK
R<$*> <$*>		$#error $@ 5.7.1 $: "550 no dot..."

-- 
|-----< "CODE WARRIOR" >-----|
codewarrior@daemon.org             * "ah!  i see you have the internet
twofsonet@graffiti.com (Andrew Brown)                that goes *ping*!"
werdna@squooshy.com       * "information is power -- share the wealth."