What is dnswl.org?
Dnswl.org is the leading whitelist provider for email filtering. It has over 80'000 users and contains more than 150'000 entries of "good mailservers".
Your email filter should try to avoid tagging messages as spam if they come from one of those good mailservers, which are assigned into one of four trust levels:
What does it cost?
Access for non-commercial users doing less than 100'000 queries per day is free. See the license page for details.