While some of you work on SPFID drafts for RFC822 From: header, I wanted
to run by others a different idea. Usually I advocated putting MARID
records into INADDR tree (as a resource to indicate if the ip should
be acting as SMTP client), the idea I have right now is to put MARID
records instead into domain of the PTR record for the ip.
This avoids problems you otherwise encounter with INADDR tree while preserving
basicly same functionality. Additionally I propose this to be used in
conjunction with EHLO checking - if EHLO listed domain does not have
record indicating if it can act as SMTP client, then server can perform
same kind of lookup for domain it obtains by doing PTR query for the
connecting ip and it asks there if that ip can act as an smtp client.
This is pretty simple and should be effective against zombie computers
which in my view is the biggest problem and supports majority of spam
and that should be solved, the sooner the better.
Here is a practical example how this might work:
$ nslookup -querytype=PTR 216.151.192.4
4.192.151.216.in-addr.arpa name = wwwtelnet.elan.net.
$ nslookup -querytype=TXT wwwtelnet.elan.net
wwwtelnet.elan.net text = "v=spf1 -all"
$ nslookup -querytype=SRV _sa._smtp._tcp.wwwtelnet.elan.net
_sa._smtp._tcp.wwwtelnet.elan.net service = 0 0 0 2.0.0.127.IN-ADDR.ARPA.
P.S. For those who don't like PTR and INADDR tree in general, I note that
AOL for one already requires that servers that connect to it have
valid PTR name. But valid name is not the same as valid smtp server
or the other way around.
--
William Leibzon
Elan Networks
william(_at_)elan(_dot_)net