[Dshield] Denying incoming email by reverse lookup of ISP DHCP-ed addresses

Michael Thompson mike at thompsonmike.co.uk
Fri Jun 17 16:19:08 GMT 2005


On Friday 17 June 2005 16:46, Stef wrote:
> You all know how some of the ISPs started denying email from what are
> home-based accounts, probably by doing a reverse lookup on the
> incoming IP, and looking for strings "hinting" on the dynamic nature
> of that IP assignment (e.g.

Just use a dynamic IP blacklist.

ie dul.dnsbl.sorbs.net

Dont know about other MTA's but in postfix, use something like this

smtpd_recipient_restrictions =
        permit_sasl_authenticated,
        permit_mynetworks,
        reject_unauth_destination,
        reject_invalid_hostname,
        reject_non_fqdn_hostname,
        reject_non_fqdn_sender,
        reject_non_fqdn_recipient,
        #reject_unknown_sender_domain,
        reject_unknown_recipient_domain,
        check_helo_access hash:/etc/postfix/helo_checks,
        reject_rbl_client relays.ordb.org,
        reject_rbl_client opm.blitzed.org,
        reject_rbl_client list.dsbl.org,
        reject_rbl_client sbl.spamhaus.org,
        reject_rbl_client cbl.abuseat.org,
        reject_rbl_client dul.dnsbl.sorbs.net,
        permit

-- 
Mike

To see the world in a grain of sand,
and to see heaven in a wild flower,
hold infinity in the palm of your hands,
and eternity in an hour.

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