Introduction
They are updated hourly and maintained by a team of experts. What are RBL blacklists? RBLs (Real-time Blackhole Lists) also offer different levels of sensitivity. Some block emails only from known malicious domains, while others also block emails from domains that are likely to harbour malicious activity.
Some also offer the option to block emails from domains that are likely to harbour spam.
To block emails from malicious domains, the domain must be blacklisted by RBL. If you use a hosted solution, you can also activate the option to block emails from domains that may harbour spam.
If you use a self-hosted solution, you can also enable the option to block emails from domains that may harbour malicious activity.
What are RBL blacklists?
What are RBL blacklists?
What is a DNS blacklist?
A DNS blacklist (DNSBL) is a mechanism for publishing a list of IP addresses that some people may want to avoid and in a format that can be easily queried by programmes on the Internet. They are mainly used to publish lists of addresses that are known to be involved in spam activities. All mail servers can be configured to reject or flag messages that have been sent from a site listed on one or more such RBL blacklists.
This RBL blacklist is an effort to stop email spam. It is a "blacklist" of locations on the Internet that are notorious for sending email spam. The locations consist of IP addresses that are most often used to publish the addresses of computers or networks linked to spam. Most mail server software can be configured to reject or flag messages that have been sent from a site listed on one or more of these lists.
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RBL Blacklists
RBL email blacklists are everywhere. There are so many that your server's IP address is most likely on one of them right now. If your server's IP gets on these email RBL blacklists, you will most likely have email delivery problems.
There are many email RBL blacklisting tools that have a long list of real-time DNS-based RBL blacklists (DNSRBL) included. However, there are only a few email RBL blacklists that we really need to worry about.
The rest of them are rarely used and it is likely that your emails are not affected by them. We will therefore explain in more detail the RBL blacklists that you should avoid at all costs.
Composite Blocking List (CBL)
This list is maintained by Spamhaus. It only displays blacklists of IPs that exhibit malicious behaviour, such as spam bots, dictionary attacks, open proxies and similar attacks.
Go to CBL Lookup Utility to check if your IP is on the list. If it is, you will be given the option to request removal.
The removal process from this list is easy. You only have to submit your IP for removal, but if your system keeps sending spam, it will be added again and quickly.
Spamhaus Block List (SBL)
The SBL Spamhaus list includes email spam operations, sources and services. They also use spamtraps - email addresses that do not belong to real users. If your server or website is hacked, spammers will often flood your system with thousands and thousands of emails. If an SBL spamtrap gets noticed, your server's IP will be blacklisted.
The removal process can vary and is sometimes not so simple. You can use the Spamhaus Blocklist Removal Center for more details on the removal process. The exact process depends on the lists (SBL, XBL, PBL) you are on. In some cases, only your service provider, who controls the IP range, can request the deletion.
XBL Exploits Blok List
The XBL lists mainly hijacked IP addresses. While these are typically from a PC and not servers, we sometimes see servers listed on these lists. If a PC is hacked but uses your server as an SMTP gateway, or if your own server is used as a spam gateway, your server's IP may be listed in the XBL.
It is good to know that the removal process in this list is easy. You can use the Spamhaus Blocklist Removal Center for more details on the removal process.
Spamcop
Spamcop mainly uses spamtraps and spam reports to generate a reputation score. If your score drops too low, your IP will be included in their list. Generally, if your IP is on this RBL blacklist, you have a security problem. It indicates that a website or user is sending hundreds or thousands of spam messages.
The removal process for this list is automatic. Unlike other providers, there is no manual removal process for Spamcop. Since they use a scoring mechanism, they will automatically remove your IP once you stop the source of the spam. Usually removal from this list occurs within 48 hours after the spam is stopped.
Barracuda
This is the RBL blacklisting resource that powers the popular Barracuda Anti-spam devices. They also make their list available for others to use via Barracuda Central. Many web hosting systems, such as cPanel, use this list by default. Most IP addresses are listed by sending spam directly to Barracuda Reputation System detectors. These are honeypots, spamtraps, and other systems that allow Barracuda to identify spam sources. As with other lists, your inclusion on this blacklist is often due to a security problem on your server.
The removal process is very easy. Simply fill in the removal request, and you will normally be removed within 24 hours.
But why these RBL email blacklists?
Based on research by Return Path, Sendgrid, Proofpoint and other major email service providers, these email blacklists have been shown to influence email deliverability to Yahoo!, Gmail, Microsoft and other major providers. If your IP is on the lists, especially the Spamhaus lists, you will have major deliverability problems with your emails.
Spamcop & CBL are used by default in many shared hosting control panels such as cPanel. If you are a small business, you will most likely have your email with a shared host using these email blacklists. WHM / cPanel supports the Spamcop and Spamhaus Zen lists. The Zen list is an aggregated list of the entire Spamhaus list which also includes the CBL.
Barracuda is used by a number of larger companies and cloud-based email security services. If you are doing business with larger companies, you may be protecting your email with a Barracuda anti-spam appliance. Barracuda also makes your list available to others. So even if the recipient server isn't using your device, they could still be using your data.
There are websites where you can check if your IP is listed on some RBL blacklists. Some of them are: rblwatcher.com or anti-abuse.org. If you are experiencing delivery problems with your emails, it is recommended that you use these sites to check that you are not on RBL blacklists.
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