Author: Adam D. Barratt Date: To: exim-users Subject: Re: [Exim] where is this evident security option in Exim ?
"Vincent" wrote, Wednesday, August 20, 2003 12:00 PM
> The idea is to stop accepting mails from any server. I just want to
> accept mail from "official" servers. I mean servers which are in the
> MX records of the domain the mail is originating.
That will not, and cannot, work. An MX record says "this host accepts
*incoming* mail for this domain". That in no way implies that such hosts
generate or handle outgoing mail for that domain, nor that any other host is
not capable of generating perfectly valid outgoing mail for that domain.
> For example, mail with From as xxx@??? coming from
> mx1.mail.yahoo.com or mx2.mail.yahoo.com or
> mx4.mail.yahoo.com is Ok.
> But mail with From field as xxx@??? coming from
> not.good.server.com is not OK.
Why not? There is absolutely no connection between From: and the host from
which mail was sent. SMTP e-mail is not designed to support or imply any
such connection (yes, I know there are a number of ideas out there that
attempt to, but none of them is part of SMTP, nor standardised).
