Oh, blacklists. With over 300 of them publicly available, it’s no wonder good senders keep a close eye on their IP and domain activity.
Public blacklists are created by large, trustworthy companies, as well as small, independent networks. But since anyone can create a blacklist, they don’t all have the same impact on deliverability. Mailbox providers and filtering companies do not leverage every blacklist in making inbox placement decisions. Instead, they typically combine data from various public blacklists, as well as data from their own networks, to determine your credibility as a sender.
Email marketers often associate blocking with being blacklisted. It’s important to note that blacklist providers are not the ones blocking your mail—it’s the mailbox provider leveraging your blacklist status that blocks your mail. If landing on a blacklist does lead to having your mail blocked, focus on the potential causes for the listing. Blacklisting is most often caused by poor list quality and end user complaints.
There are two types of blacklists: IP address-based and domain-based.
Real-time Black Lists (RBL) and Domain Name Server Black Lists (DNSBL) are lists of IP addresses whose spam status changes in real time. Mailbox providers check these blacklists to see if the sending server is managed by a sender who allows others to connect and send from their system (open-relays). They also check for known spammers or mailbox providers that allow spammers to use their infrastructure. Commonly known RBL/DNSBLs include:
URI Real-time Blacklists (URI DNSBL) are lists of domain names that appear within the email body. This blacklist will look for the URLs within the body of the email to see if it contains a domain identified as a source of spam. The most commonly used URI DNSBLs include: