Giuliano Gavazzi writes on 11/21/2003 3:12 AM:
> 2) more importantly, one can set his return address to a valid
> yahoo/hotmail address but use his own ISP SMTP server to send mail.
> You would reject these messages. This is not too common, but how
> uncommon is it?
That is not a problem. Where your approach fails is .forwards where
your user has (say) a mail.com / bigfoot / shell account pointing to his
account on your domain. Someone from hotmail mails him on that shell
account.
> A safer approach is, independently from the sender domain, check the
> HELO argument, if it contains (yahoo|hotmail)\.com check the reverse
> DNS, if the reverse does not contain the same string, defer it. Use
If HELO yahoo.com comes from an IP with non yahoo rDNS, DENY - don't
waste time deferring it.
srs
