A blacklist, or specifically a DNSBL (DNS-based Blackhole List) is a service operated by a party with the intent of restricting mail traffic from various domains to users who subscribe to that DNSBL. Criteria used to determine whether an IP address is to be listed is not standardized and is therefore up to the list maintainer to determine. The end result are lists that often use arbitrary or unreasonable criterion, sometimes even in conflict with those of other lists. Below we have compiled notes on various blacklists for your reference:
The best methods for staying off blacklists in general is to maintain a tight rein on users on your mailing/distribution lists and provide an easy way to opt-out of future mailings. Lists purchased from email harvesters are a sure-fire way to land yourself on most major blacklists and furthermore is in violation of our AUP. Best practice is to gather subscribers based on a double opt-in process, publish SPF and DKIM records, and ensure you have valid and matching forward and reverse DNS records. Details on mailing best practices are detailed in the article below.
If you find that you are listed in a DNSBL and have attempted to follow the guide's recommendations, please email email@example.com with your removal request and we will be happy to forward it to the appropriate DNSBL maintainers on your behalf.