SPF records in reverse zones?

Mark Andrews marka at isc.org
Wed Dec 5 23:55:42 UTC 2012

In message <alpine.BSF.2.00.1212052345240.58673 at bikeshed.isc.org>, Dan Mahoney w
> On Thu, 6 Dec 2012, Karl Auer wrote:
> > This may be a silly question, but are SPF records supposed to be
> > supported in reverse zones? I'm thinking of a mail server that has no
> > entry in the DNS.
> Well, most mail servers will reject such a server (i.e. one with NO rdns).  
> However, there's another possible interpretation of your request.
> SPF records go in the zone of the envelope-sender.  So if your server's ip 
> is, and your mail address REALLY is 
> bob at, then the reverse zone would also need to 
> have an MX and possibly an A record, in order to route mail to it, which 
> goes a far cry from being "a server that has no entry in the DNS".
> I can't even imagine what spamfilters would think of such an address. :)

There are some people who actually do that.
> -Dan Mahoney
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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