On Tue, 3 Oct 2006, Ramprasad wrote:
After RBL checks, what is the point in doing SPF checks if you are going to
block the email anyway?
So a SPF lookup is heavier than a rbl lookup ?
Potentially. RBL is one dns lookup. SPF is one dns lookup which after
parsing may require additional ones.
My recommendation if you're doing large-scale antispam system is to
do SPF lookup in parallel with RBL lookups. If one or more of them
give fail results that you consider final by itself, all additional
processing can stop.
But one should also note that to start doing RBL lookup you don't
even need established TCP session - you can initiate RBL lookups
immediately after you receive a connection request from some ip
address. You can either wait for RBL to provide positive an answer
or immediately allow a connection but still continue to do RBL
related processing. Chances are by the time you get to MAIL FROM
(i.e. when you can actually to SPF lookup) your RBL related
processing would be done (or you can wait for a few more packets
until RCPT TO and only then give a 500 reply if either RBL or
SPF lookup failed).
--
William Leibzon
Elan Networks
william(_at_)elan(_dot_)net
-------
Sender Policy Framework: http://www.openspf.org/
Archives at http://archives.listbox.com/spf-discuss/current/
To unsubscribe, change your address, or temporarily deactivate your subscription,
please go to http://v2.listbox.com/member/?listname=spf-discuss(_at_)v2(_dot_)listbox(_dot_)com