Max. Number of char in a TXT Record

Darvin Denmian darvin.denmian at gmail.com
Fri Mar 27 12:27:03 UTC 2009


I thank everyone for the responses.
Thank you for your spending a little time with my question.

On Thu, Mar 26, 2009 at 9:11 PM, Vincent Rivellino <vince at cuz.cx> wrote:
> On Thu, March 26, 2009 19:19, Kevin Darcy wrote:
>>> 2) What is the maximum number of includes inside a SFP field?
>>>
>> I assume you mean SPF (Sender Policy Framework), the anti-SPAM(ming)
>> mechanism (?)
>>
>> I'm no SPF expert but in glancing at the documentation it looks like
>> there is no arbitrary limit on the number of "include"s. Since SPF
>> "records" are stuffed into (one or more?) TXT records, the above limits
>> in the answer to question #1 would apply.
>
> Kevin, it looks like you are correct.  From the RFC:
>
> --------
> 3.1.4.  Record Size
>
>   The published SPF record for a given domain name SHOULD remain small
>   enough that the results of a query for it will fit within 512 octets.
>   This will keep even older DNS implementations from falling over to
>   TCP.  Since the answer size is dependent on many things outside the
>   scope of this document, it is only possible to give this guideline:
>   If the combined length of the DNS name and the text of all the
>   records of a given type (TXT or SPF) is under 450 characters, then
>   DNS answers should fit in UDP packets.  Note that when computing the
>   sizes for queries of the TXT format, one must take into account any
>   other TXT records published at the domain name.  Records that are too
>   long to fit in a single UDP packet MAY be silently ignored by SPF
>   clients.
> --------
>
> So, it appears that you can as many include's in a SPF record as you wish,
> but it would be wise to keep the size of the SPF record below ~450
> characters.
>
> There is lots of good SPF information at www.openspf.org
>
>
> -Vince
>
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