This is how I see it. SPF has to convince two sets of people.
On one publishing side there are a million domain owners.
On the lookup side there are ten MTAs.
If we want the world to use this, our tradeoffs have to favour the
multitude.
What's easy to read is hard to write.
What's easy to write is hard to read.
There are many more domain owners than MTAs. Let's make it easy for a
million domain owners to write SPF, since only ten MTAs have to read it.
IP-only notation is simple.
IP-only notation is elegant.
IP-only notation is good.
A baroque notation is worse.
And worse is better.
Eric Allman wrote:
| Regarding extra DNS lookups: even if you feel you need to retain all
| the other methods, you should at least STRONGLY RECOMMEND that only
| ip4 and ip6 be used. This isn't just to save the sender's DNS
| servers, since excess lookups tend to stress the entire system (i.e.,
| Internet), so decisions you make here can have a much wider impact
| than you think.
I can certainly add a recommendation that domain publishers precompile
their records into ip4 notation to save overhead.
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