Blacklists or Blocklists

Over 300 in use
Examine message headers for listed IP addresses or DNS
Highly subjective and arbitrary
Often difficult to resolve issues
Subscribed to by ISPs and corporate IT departments
e.g. -SpamCop,SpamHaus,LashBack, NJABL.org
A blacklist site you can check:
http//openrbl.org

Proof of permission can help you negotiate negotiate.