Date: Thu, 15 Apr 2004 11:31:16 -0500 From: Martin McCormick <martin@dc.cis.okstate.edu> To: freebsd-questions@freebsd.org Subject: Setting Sendmail to Refuse Possibly Forged Headers Message-ID: <200404151631.i3FGVGOf005743@dc.cis.okstate.edu>
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The sendmail that comes with FreeBSD is set to disallow all third-party relaying which is wonderful and how I want to keep things. In addition to that, I would like to try to set it to refuse incoming mail with forged address headers. Judging from the logs, it seems to be pretty good at catching such messages and most of the ones I look at that trigger this warning are spam. I get over 100 spam messages a day and bogofilter and junkfilter catch about 80 to 90% of them, but it would be nice if they didn't even successfully deliver. Successful delivery may, itself trigger more spam. After reading the man pages on sendmail.cf, I am not sure if I can safely do that or not. Much of the information is actually how to allow certain types of relaying. Fortunately, I don't need to loosen anything. Refusing mail from bogus addresses is slightly risky because innocent mail senders may get bitten if something is wrong with their local domain name server causing the reverse lookup to fail. I will just have to try it set that way for a while and see if anyone has trouble who shouldn't. Thanks for any suggestions or for any documentation that describes how to safely refuse forged Email without either turning on more relaying or creating any other insidious situation that might not be obvious. Martin McCormick
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