Re: [sitefinder-tech-discuss] A technical question

[Andrew Newton <anewton@verisignlabs.com>]

Kee Hinckley wrote:
> First of all, in this particular case my primary concern is whether or 
> not the domain in question can conceivably receive email (insofar as one 
> can tell short of trying to connect to a mail server).
>
> Previously the query would be pretty straightforward.
> 1. If NXDOMAIN, the answer is no, bail.
> 2. If A record exists, answer is yes, bail.
> 3. If MX record exists, answer is yes, bail.
> 4. No.
>
> Now we have a more complex situation.
> 1. If any of the A records for this domain are different from any of the 
> A records for *.tld, then the answer is yes, bail.
> 2. If any of the MX records for this domain are different from any of 
> the MX records for *.tld, then the answer is yes, bail.
> 3. No.

It is my understanding that the MX query should become before the A query.

We have talked about deploying a wildcard MX record with a target 
pointing to a non-existant name (e.g. does-not-exist.verisign.com). 
This should cause an NXDOMAIN.

We are still seeking constructive advice on this issue.

> > The service may cause a problem for a small number of spam filters 
> > that check to see if inbound e-mail is coming from a legitimate Web 
> > address, said Matt Larson, principle engineer with VeriSign's Naming 
> > and Directory Services. But the domain name check isn't used by most 
> > popular spam filters, and it's just one of many checks a spam filter 
> > vendor should use to check for spam, Larson said.
>
>
> It's not used by many spam filters because it's a standard feature in 
> all major mail servers.  Furthermore, it is on by default in Sendmail, 
> CommuniGate and probably many others.  It's a first line of defense that 
> (unlike almost all other anti-spam mechanisms) has no risk of false 
> positives.

Matt used the term "web address"?

To clarify the point:  VeriSign talked to major providers of spam 
filtering services and was informed that they do not use a forward 
domain check.

On the point of forward domain checks and false positives, I believe BCP 
30 advices against this assumption.

-andy