In <436BCC57(_dot_)1070504(_at_)de-korte(_dot_)org> Arjen de Korte
<arjen(_at_)de-korte(_dot_)org> writes:
wayne schreef:
[which is cheaper: mx vs ptr]
This depends on the MTA you're using.
Yep.
At least one (Postfix) already
performs a reverse lookup for the client connecting to it and will also
check for a matching forward record. If your MTA happens to do this too,
the PTR mechanism is essentially for free (in terms of number of lookups
required), since the neccessary lookups have taken place already.
True, if you didn't get a name server failure error the first time,
which is quite common with rDNS lookups.
This
usually will not be the case for the MX mechanism.
Unless you do things like SMTP callback verification or just simply
check to make sure the sending domain is valid.
As you said, it depends on the MTA.
-wayne
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