On Jan 13, 2004, at 10:50 AM, John Capo wrote:
Why not support both with a very strong emphasis on using _spf if the
DNS implementation for the domain allows it.
This has been discussed on this list in some detail. The short answer
is: because then you would double the work an MTA has to do for every
domain that doesn't have SPF or only has SPF at the domain level.
Again, no one would disagree with the technical merit of the idea. It
is deployment in today's internet that is the issue. This list saw
tremendous concern on the part of MTA authors about the amount of DNS
traffic required to support SPF. For big mail sites, doubling the
amount of DNS queries they make would have a major impact. SPF needs
both the MTA authors and the big mail sites on board to make it work.
There have been some technical concerns with this idea as well: I
couldn't summarize the arguments, pro and con, about negative caching
(of failed DNS lookups) and the possible mitigation and/or exacerbation
that this might have, but there were many! Please search the archives,
if you are interested.
- Mark
Mark Lentczner
http://www.ozonehouse.com/mark/
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