Date: Mon, 12 May 1997 07:51:39 +0800 (WST) From: Adrian Chadd <adrian@obiwan.psinet.net.au> To: Dev Chanchani <dev@wopr.inetu.net> Cc: freebsd-isp@FreeBSD.ORG Subject: Re: Sendmail hack Message-ID: <Pine.BSF.3.95q.970512074823.10303A-100000@obiwan.psinet.net.au> In-Reply-To: <Pine.BSF.3.95q.970511185824.21995A-100000@wopr.inetu.net>
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> I and my users have been receiving a lot of spam mail recently. Usually, > this is not so bad because I will just reply to remove me. However, more > and more spammers are using fake domain names to send their spam from. I > was wondering if you could hack sendmail to do a lookup on the reply to or > from address. If the domain name is non-existant, reject the mail. [snip] Info to do this is freely avaliable on the internet, however just add this to the end of your sendmail.cf file : Scheck_mail # Check for valid domain name R$* $: <?> $>3 $1 R<?> $* < @ $+ . > $: <OK> R<?> $* < @ $+ > $#error $: 451 Domain must resolve Note this is incompatible with the DeliveryMode=defer option, since it requires that a DNS lookup be done immediately upon mail receipt. Adrian.
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