network tests

[Miguel]

Hellow All, is there a detail explanation about the spamassassin's 
network tests?
I have only found http://wiki.apache.org/spamassassin/UsingNetworkTests, 
it says something like "*URIDNSBL: *These perform a high number of DNS 
lookups...." but without a detail about what tests are those peformed.
Right now im doing several network tests using postfix, e.g.:
- Sender's domain has mx
- Sender's mta has ptr
- Sender's  FQDN has A pointer,
etc
Does SA perform the same tests? or the network tets are related to other 
info?
Thanks