OSEC

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Subject: Re: HELO / MAIL FROM vs client
From: LaMont Jones (lamontsecurity.hp.com)
Date: Tue Jul 04 2000 - 17:33:11 CDT

> > Someone connecting from the outside to our firewall-postfix
> > and then sending mail with "MAIL FROM: someonesiemens.nl" ,
> > so that the recipient thinks that the mail really comes
> > from Siemens , which it does not.

> It is possible. However, doing so breaks email forwarding, so
> I will not spell out the details.

I remember when I first decided that it would be a good idea to reject
mail claiming to be from my domain, but originating from outside of it...
It seemed _so_ logical. It also broke mail for several people who
were trying to send mail to aliases that were housed outside of the
domain, with them as members...

The only real answer is to teach people that just because it claims
to be from Bob doesn't mean that it came from Bob, any more than it
does when the postoffice is delivering mail to your house.

lamont