On Thu, Nov 17, 2005 at 12:19:10AM +0000, David Woodhouse wrote:
> On Wed, 2005-11-16 at 16:51 +0100, Roger Håkansson wrote:
> > So I want to check that if sender domain name is in sender_local_domains
> > the user must be authenticated or host must be in relay_from_hosts.
>
> That isn't a useful test. If your users send mail to any address
> elsewhere which is forwarded back to a local user, you'll see perfectly
> genuine mail coming in from the outside but with your own users'
> addresses.
We had this problem, as the decision had been made in the past
(before my time) to block incoming from our domain. I fixed the
off-site forwarding problem by adding a signature in the mail
headers for mail sent out, and checking for it on the way in.
Can't remember exactly what it hashes right now, but I believe it
includes the e-mail address and a secret key, plus other bits. Not
100% fool-proof, but seems to work well.
I didn't like the decision particularly at first, mainly because
of the above problem, but now it seems right. Forwarding works,
and other sites pretending to send as you get blocked. Complaints
from off-site usually get redirected to
http://cr.yp.to/proto/verp.txt (We don't block on the header From).
Matthew
--
Matthew Newton <mcn4@???>
UNIX and e-mail Systems Administrator, Network Support Section,
Computer Centre, University of Leicester,
Leicester LE1 7RH, United Kingdom
