In <200606101039(_dot_)59915(_dot_)julian(_at_)mehnle(_dot_)net> Julian Mehnle
<julian(_at_)mehnle(_dot_)net> writes:
Alex van den Bogaerdt wrote:
Is this common knowledge and have people had some experience with it?
"MSN Hotmail and Windows Live Mail use a cache mechanism for Sender ID.
To guarantee your Sender ID record is included in the cache, send the
domain name(s) in a text file to senderid(_at_)microsoft(_dot_)com"
AFAIK MS's S-ID cache ignores records with variable parts, like "v=spf1
exists:%{ir}._spf.%{d3} -all", and they only use records that can be
cached. But that's only what I've heard.
I was told by Harry Katz at the New York Email Authentication Summit
last year basically what is now on the microsoft website, with the
additional tidbit that the size of the cache is finite. (I *did*
reported this info to the SPF-discuss list at the time, but no one can
remember everything.)
The 'i' and 'd' macros aren't actually a problem because they can be
easily cached. To quote RFC4408 section 8.1. "Macro Definitions":
Note: Domains should avoid using the "s", "l", "o", or "h" macros in
conjunction with any mechanism directive. Although these macros are
powerful and allow per-user records to be published, they severely
limit the ability of implementations to cache results of check_host()
and they reduce the effectiveness of DNS caches.
Implementations should be aware that if no directive processed during
the evaluation of check_host() contains an "s", "l", "o", or "h"
macro, then the results of the evaluation can be cached on the basis
of <domain> and <ip> alone for as long as the shortest Time To Live
(TTL) of all the DNS records involved.
It is my understanding that this text was included by MarkL at the
request of Microsoft.
-wayne
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