Hi Chris, Yes. If you don't allow relay, then the server will not relay. You can also do other things like prevent the machine from resolving Internet host names (just for fun). HTH, Tom Thomas W Shinder www.isaserver.org/shinder <http://www.isaserver.org/shinder> ISA Server and Beyond: http://tinyurl.com/1jq1 Configuring ISA Server: http://tinyurl.com/1llp <http://tinyurl.com/1llp> -----Original Message----- From: Allen, Chris [mailto:CAllen@xxxxxxxxxxxxxxxx] Sent: Friday, September 26, 2003 8:34 AM To: [ExchangeList] Subject: [exchangelist] Relaying question http://www.MSExchange.org/ Per SpamCop and SpamHaus, "Spammers are taking advantage of weak passwords on systems using smtp/auth and brute force finding name/password combinations that work and then sending spam thru these servers. There are various characteristic footprints for this and one of them is the use of a "from" address of the format bluestallnn@some legit ISP and the "nn" iterates in each successive spam. bluestelllf@xxxxxxx bluestellpg@xxxxxxxxxxx bluestelluf@xxxxxxxxx " My question is this, if I uncheck "Allow all computers which successfully authenticate to relay, regardless of the list above", will this effectively stop brute force attacks on weak passwords as far as exchange is concerned and what will this break? I am also taking measure by blocking their entire block of IPs. The ranges are as follows: 211.158.32.0/20 211.158.48.0/21 211.158.80.0/20 219.153.144.0/20