email validation tools

Email Blacklist Check

What exactly is an email blacklist check? It sounds a bit like rocket science, but it is actually quite a simple topic to understand.

Imagine that Cindy sends an email to Fred from [email protected]. Fred’s email server determines Cindy’s IP address and then resolves it to the domain. Fred’s email server double checks Cindy’s IP address and her domain up against their domain and IP blacklist data set. Are you with me so far? Great, let’s keep going!

Suppose the results from Fred’s email server comes back with a positive match for Cindy’s IP or her domain… No Bueno… This means that Cindy’s email will land in Fred’s spam folder. However, if Cindy’s domain or her IP have already been flagged as spam several times, then Fred’s ISP will completely block this email and Cindy’s email will not even reach Fred’s spam folder at all. Hopefully that is a clear workflow?

Well, how did Cindy’s IP or domain even end up in a database that has blacklisted her? Typically it is because the emails you send are considered to be spam. Who determines this? There is not a central blacklist authority, blacklists are managed independently and each email blacklist has their own criteria for how you get on their list and how you get off their list. Again, the main reasons for landing on a list and needing to even review an email blacklist check are because you are flagged for sending a virus, malware or spam. The latter often happens due to improper proper email list cleaning, or from purchasing lead lists or other email lists that have incorrect or non-relevant email addresses (thus you get flagged for spamming). 

There is also a risk of your email getting hacked and someone sending an email (or thousands) from your account, which can land you on an email blacklist too. It could also be that you are on a blacklist due to your website being viewed as spam and being in a search engine black list. Typically this happens from black hat SEO or other unscrupulous marketing activities. Lastly, it could be the IP getting blacklisted due to the person that was on that IP prior to you or someone on a shared IP connection. In a nutshell, blacklists for IP and domains are used to provide a better user experience and to eliminate garbage, or malicious content from landing in your email inbox.

Let’s dig in a bit more on the types of email blacklist checks.

Domain Name System Blacklists (DNSBL), is an email blacklist that allows the admin to block emails from a particular IP with a historical spammy track record. This list is focused on the DNS (Domain Name System). The DNS translates the IP address into the domain name for the end user.

There are a bunch of DNSBL’s online, they have their own rules and reasons/offenses that might fit their criteria for you to get blacklisted and be on their list. Offenses could include malware, hacking, SPAM, etc. from an IP. Email administrators use DNSBL’s to review whether the inbound email came from a blacklisted email or not. In a nutshell this is an email blacklist check and rejection.

Let’s move on to the SURBL.

SURBL is a collection of URI DNSBL lists of Uniform Resource Identifier (URI) hosts, typically web site domains, that appear in unsolicited messages per wikipedia. What does that mean? It means that email messages are scanned to detect websites they reference and check them against blacklists. If those websites are found, then appropriate action is taken, like flagging as SPAM or by rejecting the email altogether.

Hope you aren’t showing up on any email blacklist checks, but if you are, can you get off one?

Yes, but it’s not as easy as just pushing a big red button. You need to find out where you are blacklisted and contact them. This is of course provided you either cleaned up, or stopped doing whatever it was that got you on their email blacklist in the first place. Most blacklists allow you to submit a removal request, but they are all independent, so each list has its own removal request workflow. That’s it, we hope this made sense and was helpful. Feel free to sign up for our free account to get started with your email validation needs.


Are you having trouble, have some questions. How can we help?