please carefully read complete article: Spamassassin Other Tricks
some tips for this:
Simple way to check the MX-Records (and the other records of course) of a host should be:
Now have a close look on the different mailservers (MX records).
The value after "by" is the so called priority of each entry.
Notice the point at the end of aspmx.l.google.com. and the other mailservers. This called root-label, which does not have a formal name and its label in the DNS hierarchy is an empty string.
More advanced way to check for records is nslookup:
Non-authoritative answer: google.com mail exchanger = 40 alt3.aspmx.l.google.com. google.com mail exchanger = 20 alt1.aspmx.l.google.com. google.com mail exchanger = 50 alt4.aspmx.l.google.com. google.com mail exchanger = 30 alt2.aspmx.l.google.com. google.com mail exchanger = 10 aspmx.l.google.com.
Authoritative answers can be found from: alt1.aspmx.l.google.com internet address = 18.104.22.168 alt4.aspmx.l.google.com internet address = 22.214.171.124 alt2.aspmx.l.google.com internet address = 126.96.36.199 aspmx.l.google.com internet address = 188.8.131.52
use this advanced online tool, to get some informations via the world wide web http://centralops.net/co/