From owner-lir-wg@ripe.net Mon Jan 12 09:27:45 1998 From: Sami Koskinen <tossu@katiska.clinet.fi>
On Fri, 9 Jan 1998, Poul-Henning Kamp wrote:
One of the best things to do, would probably be to make a simple turnkey kind of sendmail config available to people.
What I think as the best solution is to patch sendmail to check from the name service if we really are in the mx list for the incoming mail. This would eliminate the need to store the same information to some other place, as we already have the information stored in the name service.
The idea is good indeed. I am, however, somewhat concerned about the following potential dangers: 1. The DNS can contain bogus info (including MX records). 2. You could be a victim of a malicious setup. For example, the primary of foo.domain puts an MX to one of your hosts protected in the way you suggest. When the secondaries have updated the zone, you get a large number of spam destined for foo.domain. Your resources may be abused, and you can even suffer a DoS. (At the same time, foo.domain may even filter out SMTP connections from you, to make sure *his* resources are not wasted...). To summarize, I feel it would be very good to use the info in the DNS, (in order to avoid redundancy in configuration and possible misconfigurations), however the DNS data may not be trustworthy, especially for the zones you are not authoritative for. One should balance between the advantages the suggested patch would bring and the dangers it exposes the user to... I personally would feel more confortable to explicitely allow myself the domains I want to relay, in spite of the extra work and possible misconfiguration. Just my 0.02$. Janos