[Mimedefang] SURBL effectiveness and domain turnaround time

[David F. Skoll]

On Wed, 8 Sep 2004, Jeff Rife wrote:

> This is a good thought, but caching of DNS records defeats this.  I
> know that most BLs have low TTL in the records, but lower than about an
> hour would cause a lot of extra network traffic, especially on the "not
> found" responses.

sc.surbl.org seems to have a 15-minute TTL.  And the negative-response
caching TTL is under your control.

DNS lookups are pretty cheap -- one UDP packet out and one UDP packet back
in.  (Unless you use Microsoft's bloated Sender ID XML garbage that
probably forces you to use TCP for your queries.)

sc.surbl.org has 13 name servers, just like the root name servers of
the Internet.  You can imagine that if 13 name servers can handle all
the root name server traffic, it's not so bad to have a low TTL. :-)

Regards,

David.