spf-discuss
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Re: Eric Allman comments on SPF

2003-12-13 09:33:51
If Allman's concerns are solely about complexity, then drop include: redirect= and macros, or at the very least make them MAY rather than MUST. I don't think A, MX, and PTR mechanisms are any more complex than IP4.

If his concerns are about performance, that multiple DNS lookups need to be performed in sequence, then we should do what some BIND implementations do with MX records: send additional information in the response that are going to be asked for anyway.

An MX lookup for 'wayforward.net' on my server returns:
        wayforward.net  preference = 40, mail exchanger = mail.wayforward.net
        wayforward.net  preference = 30, mail exchanger = mx1.wayforward.net
        mail.wayforward.net     internet address = 209.208.196.229
        mx1.wayforward.net      internet address = 69.55.226.139

All these entries are (presumably) cached, so when a mailserver does the 'A' query for 'mx1.wayforward.net' the response is immediate.

So, when the SPF DNS resource type is supported, DNS server implementations SHOULD send additional info: A records if the SPF record contains an A mechanism, MX records if the SPF record contains an MX mechanism, etc.

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