Please try this on your mail server. I have already tried it on many servers, including postfix and sendmail. All are vulnerable. telnet mailhost 25 helo hostname mail from: <> rcpt to: user@mailhost data ... the important things are - 1. the mail from address is blank: <> 2. the rcpt to addresses are within the mail servers domains so relay is not a problem This allows spammers to send mail using a null return address. In the mail, the address gets translated to MAILER-daemon. To fix it in sendmail, go down to ruleset 3, search for a line that starts with R<> It should look like this: R<> $@ < @ > MAIL FROM:<> case change it to this: R<> $#error $@ 5.1.3 $: "User address required" That should block anonymous senders. Any idea why this is allowed (there is a special rule to allow it) at all? Philip -- Repel them. Repel them. Induce them to relinquish the spheroid. - Indiana University fans' chant for their perennially bad football team Visit my webpage at http://www.ncst.ernet.in/~philip/ Read my writings at http://www.ncst.ernet.in/~philip/writings/ MSN philiptellis Yahoo! philiptellis