Re: More about the SPF RRTYPE

On Mon, Aug 15, 2011 at 4:00 PM, Frank Ellermann
<[email protected]> wrote:
> On 15 August 2011 21:06, Murray S. Kucherawy wrote:
>
>> Over on the exim-users mailing list, someone just complained that
>> libspf2 tries for RRTYPE 99 (SPF) before 16 (TXT).  That’s what the
>> standard says to do, but it also means some sites that firewall out
>> unknown RRTYPEs cause clients to time out on the 99 before they try
>> 16.  During that time, some SMTP clients time out altogether and
>> try again later, and the mail ultimately never gets through.
>
>> Maybe this isn’t news to anyone
>
> Yes, but it is clearly something that should be addressed in 4408bis:
>
> Apparently nobody intends to eliminate the ugly TXT abuse in v=spf1,
> because it's years too late to try it, or IOW, the wannabe-experiment
> failed to fix this.
>
> Possible ways to improve that situation in 4408bis:
>
> 1 - try the SHOULD type 99 approach again, a PS could succeed where
>    an "experiment" failed.
> 2 - give up, note that TXT is ugly but can't be changed, and that
>    now is the time to drop SPF type 99 for the purposes of v=spf1.
> 3 - explain that practical EDNS0 limits could affect TXT where type
>    99 still works, but that trying both queries simultaneously and
>    pick the first answer is perfectly okay.
>
> I didn't look into RFC 4408 for some years, but IIRC (3) is allowed,
> or isn't it?
>
> -Frank
>

4.4.  Record Lookup

   In accordance with how the records are published (see Section 3.1
   above), a DNS query needs to be made for the <domain> name, querying
   for either RR type TXT, SPF, or both.  If both SPF and TXT RRs are
   looked up, the queries MAY be done in parallel.


We may want to change the MAY to a SHOULD.