Email blacklists are lists of websites or IP addresses that are blocked by an email server. When an email comes from a blacklisted sender, it is restricted from entering a user's inbox. All email servers maintain a blacklist because these websites or IP addresses send out unsolicited and spam mail.
Blacklists prevent spam from entering a user's inbox. Without blacklists that work with spam filters, your email inbox might have hundreds or even thousands of junk emails. The blacklist allows users to automatically block what might be spam and viruses. Blacklists also prevent phishing emails, where a scammer tries to collect a user's personal information to resell. Blacklists help your email system function smoothly.
How It Works
For the most part, blacklists are created by users. Once you filter, reject, or junk a mail, then the email ID is scrutinized by the server. If the server deduces that the email is junk, then the IP address or website will go on the blacklist. Sometimes, email blacklists come preinstalled with your spam software. Your spam software will automatically update this list periodically.
Email blacklists work through the Domain Name System (DNS) used by the email server. When you receive an email, the email server checks whether the Internet Protocol (IP) address belongs to the blacklist. If it does, it will be blocked from entering your inbox and will bounce back to the user.
There are two basic methods that can be used to create email blacklists: local lists and distributed lists. A local list is a list of mail ids or IP addresses that are maintained by a specific organization or website. The addresses are manually entered by the administrator of the website to the blacklist. Distributed lists or third party lists are a listing of IP addresses that are publically available. A particular network or IP address may be blocked by the third party list, but you will stop receiving mails from that website only if you enter it in your blacklist.
You can check if an IP is blacklisted by entering the address and submitting it to websites that maintain a list of ids. These websites also act as tutoring networks to help you protect yourself from spam and to prevent your organization from ending up on a blacklist. It also gives you ideas on how to remove yourself from a blacklist.
Almost every mail service provider has an application that can be used to create blacklists. Leading email blacklist tools include SORBS and Blacklist Monitoring.