What is a Blacklist?
Depending on the source, the amount of daily spam emails being sent is anywhere between 80 and 95% of all emails sent on the internet that day. With such large numbers, most experts agree that manually sorting through your inbox to get rid of spam has become highly inefficient these days. As such, public blacklists of mail servers and IP addresses have been created to prevent repeat offenders from relaying spam.
A blacklist is a list of blocked domains, email addresses or IP addresses. When a website gets on one of these lists, users can no longer access the site directly and servers that use these blacklists will block emails from the domain.
The operators of some of the biggest blacklists, Spamhaus have created this chart to make it easier to understand how and when the blacklist interacts with the email:
There are public blacklists, which as the name suggests, are available to everyone to filter email, while private blacklists are maintained by third-party organizations. To find out more about domain blacklists, read our article on what are DNSBLs (Domain Name System BlackLists).
How do I know if I am on one?
There are countless tools available online that have access to hundreds of different blacklists databases and will run your domain/email/IP address through them to determine if it is present on any. If the result comes back positive, don’t panic! There are hundreds of blacklists around the world and if you partake in any form of email marketing, chances are, your IP is on at least one of them.
How did I get on one?
Different blacklists have their own criteria on what lands you on their list, however in most cases, it could be narrowed down three main types of criteria:
- Technical - Policy - Evidence-based
Technical: could happen from server misconfiguration, DNS record errors, missing banners, etc. the reason why these issues are blacklisted is due to the fact that many of these issues are signs of an existing malware on the server, which are more often than not present without the owner’s knowledge.
Policy: Sometimes entire internet service providers (ISPs) and even countries are blacklisted. Your domain may be simply in the region affected by the policy.
Evidence-based: occurs when the blacklist operator has direct or indirect evidence that a domain is sending spam emails.
There are also some common triggers that lead to blacklisting:
- A sudden surge in email sending volume occurs
- High Spam complaint rates
- Poor email list hygiene
- Bad content (certain words or phrases that express spam-like content
How do I get off a blacklist?
Being listed on a smaller list is not that much of a concern as for the most part, it won’t impact your ability to communicate with your customers too much. However, if you land onto one of the bigger lists, used by ISPs to filter spam, it can have quite an impact on your emails being delivered and thus, your business.
If you’re blacklisted and believe you shouldn’t be, you will have to take action to have your IP removed from the said list. Most DNSBLs will have clear instructions on how to get your domain off their list. This is done through a process called delisting and is done by directly contacting the operators of the list and requesting a removal.
Some things to keep in mind when delisting:
- If you are a repeat offender, it gets more difficult to get off the list, at times even impossible.
- Being on the blacklist means that you have matched the operators’ criteria and thus arguing with them over the validity is pointless. It is better to be open to criticism and work together to reach a solution.
- If you know the cause of the listing, yet haven’t fixed the issue, its best to wait until it is resolved before applying for a delisting. The operators will be more lenient if they see that the problem was fixed before the application process.
Most DNSBLs have an automated process that removes low-level listings within a certain time frame (usually 1-2 weeks). If an IP address has been listed multiple times or been sending abundantly high volumes of spam, this process may take longer or even land in the permanently-blacklisted IPs list.
Here are some of the most prominent blacklists that you should keep an eye out for:
- Composite Blocking List (CBL)
- Spamhaus Block List (SBL)
- XBL Exploits Block List
- Passive Spam Block List (PSBL)