Skip to Main Content

The Truth About Blacklists and How They Affect You

by Michelle Keegan,  Constant Contact Email Marketing Expert

I have answered a few questions about blacklists lately and I thought it would be useful to clear up some possible misconceptions about blacklists and their effect on your email deliverability.

The fact is, email blacklists, a.k.a. blocklists, can affect your email deliverability, but not as much of an impact as you may think. (I'll use the term "blocklists" from now on as this term more accurately describes the result).

Email blocklists have been around for a while. And over time, the way blocklists operate, the way they are viewed and, more importantly, used by the industry has evolved.

What is a Blocklist?

A blocklist is a list of domains or IP addresses of known and/or suspected spammers originally intended to assist ISPs and corporate domains in blocking email from IP addresses reported to have sent spam. At one time, ISPs and corporate mail administrators turned exclusively to blocklists in an effort to satisfy their customer demands and reduce the impact of spam on their servers. (See more definitions in the glossary below).

This approach was effective when spammers didn't go to so much trouble to hide their identities. Unfortunately ISPs soon found that spam could come from the same servers as good end-user email. And that the use of blocklists also caused them to mistakenly block legitimate email. The industry calls this a "false positive."

One of these blocklists is not like the other - vive la difference!

Well-maintained, reputable blocklists operate with clear listing and delisting policies. They provide reliable points of contact and their records are kept up-to-date with current information. SBL (SpamHaus blacklist) and Spam Cop are two such reputable, well- maintained blocklists. Use of these blocklists usually results in a low number of false positives.

In contrast, there are those blocklists that are maintained by individuals with their own agendas. Some are self-proclaimed vigilantes and some do not believe in commercial email of any kind. Their listing policies are arbitrary (except in cases where they list legitimate email addresses on purpose - no I'm not pulling your leg) and their delisting policies are often non-existent. Blocklists of this kind rarely provide reliable points of contact and most of them operate using outdated information. Use of this type of blocklist typically results in a much higher rate of false positives.

Any blocklist can contain legitimate email senders or email service providers. In fact, just a few spam complaints can land an IP address or an email service provider on a blocklist despite the fact that the ratio of complaints to volume of email sent is extremely low. But, in the case of reputable blocklists like Spam Cop, you can be removed from a blocklist quickly if you can demonstrate that you are a responsible permission emailer.

ISPs cannot live by blocklists alone

Some smaller ISPs and companies that lack dedicated email administrators or the financial resources to use a more reliable solution, still use blocklists alone to determine which email they deliver. This is becoming less and less common.

Because blocklists have been the target of criticism industry-wide for frequently blocking email that is not spam, most ISPs - definitely all of the larger ones - only use reputable blocklists and only in conjunction with other methods including spam complaints, content filters, whitelists and more to assist in making the final judgment call on whether to deliver or block email.

It is very common for ISPs and corporate networks to create their own custom set of criteria for blocking. Many ISPs will use information from blocklists, content filters, bounce rates and complaints in a "weighted" system that gives "spam points" for each different factor and then set a threshold appropriate for their system. All mail with "spam points" above the set threshold will be tagged as spam, thrown in the trash, or bounced back to the sender.

Email deliverability as a whole is what really matters

And your email deliverability depends on way more than blocklists.

What can you do? Use a reputable email service provider that delivers your email with the proper protocols, has relationships with ISPs and is whitelisted (whitelist is to blacklist as paper is to rock). A good email service provider has the resources and scale to reach out to the ISPs and blocklist community to get issues resolved quickly. The email marketing service you select should obey the law, maintain strong permission policies and have an active anti-blocking team working on your behalf.

Remember, blocklists are only a piece of the puzzle. So, take a walk in the archive! Read this past issue of Hints & Tips to learn how to become a trusted sender, avoid content filters and more.

Note to Constant Contact Users: Constant Contact's average email block rate is 3% compared to the industry average of 22%.

If you are a Constant Contact customer and you think your email is being blocked, go to Constant Contact Support and search under bounces and delivery for help.

Glossary of Terms

  • Email Blocking - Email blocking occurs when the receiving email server (e.g. Yahoo!, AOL, Hotmail etc.) prevents an inbound email from reaching the inbox of the intended recipient. Often the sender of the email receives a "bounce" message indicating that their email has been "blocked."
  • False Positive - A false positive occurs when a legitimate permission-based email is incorrectly filtered or blocked as spam.
  • Filters - "Filtering" is a technique used to block email based on the content in the header, "from:" line, "subject:" line, or body copy of an email. Filtering software searches for key words and other indicators that identify the email as potential spam.
  • Blacklist a.k.a. blocklist - Some ISPs use a blocklist to help them determine which emails should be blocked. Blocklists contain lists of domains or IP addresses of known and suspected spammers. Unfortunately, these blocklists also contain many legitimate email service providers. Just a few spam complaints can land an IP address or email service provider on a blocklist - despite the fact that the ratio of complaints to volume of email sent is extremely low.
  • Whitelist - A whitelist is the opposite of a blocklist. Instead of listing IP addresses to block, a whitelist includes IP addresses that have been approved to deliver email despite blocking measures. It is common practice for ISPs to maintain both a blocklist and a whitelist.

For more definitions, refer to our email marketing glossary.

Send feedback
back to top
ESPC MAAWG America's SBDC Score Return Path TRUSTe Awards Partners
strlpa1@constantcontact.com strlpa2@constantcontact.com