What is ... deliverability? Part 2: Blacklists

29.05.2009
In my last CEO blog article, I introduced the subject of “deliverability” – click here if you missed it. Today, I intend to take a closer look at blacklists.

Before recipients receive an email from an unknown sender, the mail server checks the email carefully for spam characteristics. If there are none, the email is delivered to the recipient’s inbox.

Yet this analysis is very time-consuming. Life would certainly be easier for mail servers if they could reject emails simply by analysing the sender address and dispense with examining the content in detail. But how do they decide in the case of unknown senders?

Centralised lists published on the Internet can help with this. There are two types of lists: one for the “bad” senders and one for the “good” ones. In technical speak they are known as “blacklists” and “whitelists”. Mail servers can treat emails from “bad” senders as spam and reject them. Emails from “good” senders can be delivered immediately. Further checks are therefore only needed for unknown senders who are neither blacklisted nor whitelisted. This makes life considerably easier for the mail server.

How do blacklists work? These negative lists contain the addresses of senders whose email traffic has attracted negative attention in the past. This includes senders of spam, for instance, who normally send out emails to several hundred thousand recipients. If enough recipients of an email complain about the sender, that sender will be blacklisted. The consequence of this is that every mail server around the world that queries this negative list is forewarned and immediately treats emails from this sender as spam and rejects them. This quickly puts a stop to the spammer’s game.

Although this concept sounds simple in theory, in practice it is anything but. It is much too easy for serious senders to end up blacklisted, despite them having strictly obeyed all the rules of permission marketing. One reason for this is that many recipients click their email program’s “Report as Spam” button for convenience’s sake, instead of scrolling down to the unsubscribe link contained in the body of email newsletter. Although this achieves the desired result for the recipient and means that he/she will not receive any further emails from this sender, for the sender it can lead to a blacklisting and subsequently to global delivery problems.

The email marketers themselves are not informed of the blacklisting and it only comes to their attention indirectly from decreasing open rates and click rates and from the increasing number of undeliverable emails.

Another problem is that virtually anyone can operate a public blacklist and that there are no rules governing either the grounds for a listing, nor how serious senders can have their email address removed from the list. Some blacklists only require a handful of recipients to report the email as “spam”. Several operators also charge a fee to delete blacklistings.

Thankfully, this is something customers of our Inxmail Professional ASP Service do not have to worry about, since we take care of all matters related to blacklisting. For everyone else, we offer our Blacklist Monitor Service (www.blacklistmonitor.de). This not only informs customers when they have been blacklisted, but also offers them advice on how to deal with a listing of this kind.

In the third part of my “deliverability” series, I will be taking a closer look at “whitelists” and “reputation networks”.

Part 1: What is deliverability?

Part 3: High deliverability rates with whitelists