ietf-mxcomp
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Re: Using MX as the pointer to the other RR

2004-06-04 05:46:58


On Jun 4, 2004, at 7:32 AM, wayne wrote:


In <EB3FF3D8-B5E5-11D8-88FE-000A95B3BA44(_at_)hxr(_dot_)us> Andrew Newton <andy(_at_)hxr(_dot_)us> writes:

So he had an interesting idea.  He suggested that instead of looking
for the MARID record in the domain of the sender, look for it at the
MX target of the sender.  This solves his problem since his DNS zone
is the MX target. This also leads to a solution to the wildcard issue.


So, example.com has MX records:
example.com     MX      1 foo.com
example.com     MX      1 bar.com


Now, are you suggesting that the MARID record would have to be placed
in *both* foo.com and bar.com?  What if they conflict?  What about
mail servers out there that depend on the falling back to A records
and have no MX records?


Good questions. The top-of-my-head answers are: 1) use the same strategy as MX - if no MX is found, look at the spot where an A (or AAAA) record would be, and 2) when there are MX records, ONLY use the one with the lowest priority. Multiple MX records of the same priority do not match the given use case actions (in other words, in the given use case it is unlikely that there are multiple MX records but if there were they would all point to the same mail provider).

If it does turn out that this approach does not work, it is still probably worth the time to find an appropriate solution to the use case.

Stepping into the clouds for a second (where the air is thin, btw), this does bring up two semantic issues: 1) the inbound does not necessarily mirror the outbound, and 2) this is another example of Dave's assertion that mail paths are not site-to-site as many have assumed.

-andy