Your were probably pointed to this URL because your mail server is configured in violation of rfc822 and rfc1123. Your server probably does something like this: > 220 X1 NT-ESMTP Server mailhost.directlink.net (IMail 6.05 1039005-4) > mail from: <> > 501 bogus mail from > quit > 221 Goodbye or this > 220-rocmail.com ESMTP MDaemon 3.5.6 ready > 220-RocSoft does not allow you to relay mail. No FakeMail > 220-No SPAM, No USBE, No Telnet, Tchuessie! > 220 > helo foo > 250 rocmail.com Hello foo, pleased to meet you > mail from: <> > 550 Sorry, this server is configured to refuse this sort of mail (to combat the SPAM problem) > quit > 221 See ya in cyberspace or this > 220 mail.softagency.co.jp ESMTP > helo domain > 250 mail.softagency.co.jp > mail from: <> > 250 ok > rcpt to: > 553 sorry, your envelope sender is in my badmailfrom list (#5.7.1) ftp://ftp.isi.edu/in-notes/rfc1123.txt section 5.2.9 states: ---- The syntax shown in RFC-821 for the MAIL FROM: command omits the case of an empty path: "MAIL FROM: <>" (see RFC-821 Page 15). An empty reverse path MUST be supported. ---- Refusing mail from an NULL envelope sender: - breaks the above RFC - accomplishes very little with regards to spam prevention - prevents you from getting any bounce messages back if one of your users Emails other people with a bad address. Your server then clogs up the mail spool of the servers that are trying to send you a bounce by refusing those bounces - Last but not least, you are now going to have your Email rejected by servers like sourceforge.net because they require validation of your envelope and header sender. Those mail servers connect back to you and check the address like this: > 220 server ESMTP Sendmail 8.9.3/8.9.3/Marc v3.1 (09/04/98); Tue, 27 Mar 2001 16:08:39 -0800 > helo foo > 250 server Hello root@connectingserver [X.X.X.X], pleased to meet you > mail from: <> > 250 <>... Sender ok > rcpt to: > 250 ... Recipient ok > quit > 221 server closing connection Because you refuse the "mail from: <>", the mail server refuses your mail. BTW, this seems to be a frequent problem for Red Hat 6.2 users because apparently linuxconf 1.17 is known for generating bad sendmail.cf files. It typically looks like this: 220 hostname.dyn.dhs.org ESMTP Sendmail 8.9.3/8.8.7; Tue, 1 May 2001 23:14:37 -0400 mail from: <> 554 buildaddr: no mailer in parsed address: Error -7 The fix (outside of not using sendmail :-D), is apparently to upgrade linuxconf or generate the sendmail.cf some other way