Milter-greylist

The site http://mxtoolbox.com/ claims that my inbound mail is 
particularly slow.  The specific test page is at 
http://mxtoolbox.com/domain/www.simplesystems.org/.  The claim is that 
it takes 8.5 seconds to deliver a mail to my domain and results are 
consistent.

Yesterday I switched from early 1994 SPARC hardware (still with lots 
of memory so almost everything is in RAM) to modern 64-bit Intel 
hardware with fast SSDs and a ton of RAM.  The test page for this site 
says that the timing between the new and old hardware is almost 
identical.

I am using milter-greylist as the Milter.  Unless the test page is 
faulty, the only part of the chain which could take any time is 
milter-greylist since it does DNS queries.  However, I am not seeing 
any indicated slowness in the logs.  Only every once in many emails do 
I see a long SPF lookup (have seen 15 seconds before).

Is this test page faulty or is there something in my mail delivery 
chain (e.g. milter-greylist) which is adding time?

Bob
-- 
Bob Friesenhahn
bfriesen@..., http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/