How DNSBLs Work: Preventing Blacklisting

When you open your email client, type a message, and hit “send” it seems so easy. You don’t think about all the processes taking place in the background or security checks being run on your outgoing mail. Most of the time, you don’t even wonder if your message will make it to the recipient, or if it will be marked as spam. Email has come a long way since its early days. Today, many tools exist to help verify that a sent email comes from a legitimate IP address or domain name. But this verification is still a difficult process for email service providers. If you have your own mail server and send out messages from your domain, you don’t want your emails getting blacklisted as spam — especially if you run a business that focuses on email marketing. In this guide to DNSBLs , (Domain Name System Blacklists), you’ll learn how DNSBLs work, what to do if your domain gets blacklisted, and how to avoid getting blacklisted in the first place. A DNSBL, also referred to as a DNS Blacklist or RBL (Realtime Blackhole List), is a list of domain names and IP addresses that have a history of sending spam emails. Web administrators use DNSBLs to block messages from these addresses so that when messages get sent from these addresses, they are flagged or rejected before arriving in the recipient’s inbox. DNSBLs date back to 1997, when the first one was created. Today, almost all email servers support at least one DNSBL to reduce junk mail and spam that clients receive. The basic components of every DNSBL are: Many services today offer DNSBLs and each one has its own standards for what is considered spam. Some are stricter than others, making it relatively difficult to be removed from the blacklist once you’re on it. Some common DNSBL services include: You can see a full list of DNSBLs on our Blacklist Checker tool webpage. All DNSBLs operate on the same premise: adding spammers to the blacklist. But the policies of each DNSBL differ. How long a domain stays on the blacklist, what must be done to be removed from it, and other details vary depending on the DNSBL service you use. You can tell DNSBL policies apart by looking at three factors: Listing lifetime : Listing lifetime is how long an address stays on the blacklist once it’s added. Some services automatically expire addresses after a certain time and others require manual removal. It also refers to the policies the DNSBL has in place to allow listed hosts to get their addresses removed. Each DNSBL uses different listing criteria. Something that gets flagged with one service may not be flagged with another. For the most part, DNSBLs use the following reasons to blacklist addresses. If you run a mail server or manage one with multiple accounts, you need to ensure that your server doesn’t get blacklisted. You can look up your IP address or domain with our Blacklist Check tool . We also have a Blacklist Help forum you can visit for questions about listing and removing IP addresses on blacklists. If you suspect your IP address or domain name has been blacklisted by a DNSBL service, the first thing you need to do is figure out which service is blocking you. You can do that by using Blacklist Check tool mentioned above. Once you know which DNSBL has flagged you, you can check their website for resources or articles on how to get delisted. Most services have instructions you can follow for getting your address removed from the blacklist. You may also learn why you’ve been listed in the first place. After learning the reason behind being put on a blacklist, your next step is to remedy the action that put you there. Some steps you may have to take include: Some DNSBLs have a self-service removal feature that lets you take your address off the list yourself. Most blacklists, however, have a time-based removal. These processes automatically remove low-level offenders within one or two weeks. When you reach out to a blacklist service about getting your address removed, it’s important to be professional and follow their instructions. If you truly haven’t done anything wrong, let them know and they should be more than willing to help you get your address removed. When your interact with the DNSBL, keep the following in mind: The best way to deal with getting blacklisted is not to get blacklisted in the first place. You can do several things to prevent being considered spam or ending up on a blacklist. At this point, you may wonder if it’s possible to have your address whitelisted by a DNSBL service. In other words, no messages from your server or address ever get flagged because you’re marked as “safe.” As a general rule, DNSBL services like Spamcop, Spamhaus, and others do not allow whitelisting. If they did, it would compromise the security they’re promising to their email clients. You know that your emails are safe, but the DNSBL or users don’t. Furthermore, at some point after you’ve been “whitelisted” a spam email could mistakenly come from your address and if you are considered “safe” this email would get through to its recipient. The best thing you can do is work to avoid getting blacklisted and to cooperate with DNSBL services to get removed if you ever do end up on a blacklist. Finding out your domain or IP address has been blacklisted isn’t cause for panic, but you should take the matter seriously. If you follow some of the tips in this guide, hopefully, you can avoid being blacklisted entirely.