begin Tuesday 13 January 2004 16:15, Hallam-Baker, Phillip quote:
The big advantage to using the prefix is that the service can tell with a
single request whether a service does SPF or not, there is no need to do
any further parsing at all.
That is a huge advantage if you have a scripting type scheme, you can have
code of the form:
spf = Get_SPF_Record (domain)
if (spf != null) then
Do_SPF_Processing (message, spf)
Otherwise you have to start looking at the content of the record which is a
bit more complex.
Moreover, some environments may not be able to get all TXT records (if
several are present) but only get a random entry from the list. Case
in point: I'm right now studying the feasability of implementing SPF
as a sendmail.cf ruleset, but stumbled accross the following
restriction
(quoted from http://people.freenet.de/slgig/op_en/sendmail_cf.html#keyfile):
dns This map requires the option -R to specify the DNS resource
record type to lookup. The following types are supported: A,
AAAA, AFSDB, CNAME, MX, NS, PTR, SRV, and TXT. A map lookup
will return only one record. Hence for some types, e.g., MX
records, the return value might be a random element of the
list due to randomizing in the DNS resolver.
This means that (in sendmail.cf) there is no way to fetch all TXT
records in order to find the one that starts with v=spf1
However, I've contacted sendmail(_at_)sendmail(_dot_)org about the issue, with a
little bit of luck, they'll add a more versatile dns map in one of the
next versions ;-)
Regards,
Alain
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