A colleague sent me this link discussing the use of the word “free” in email subject lines. The gist of the article was that using “Free” in the subject line is frowned upon by savvy email marketers because of its potential of triggering spam filters, but that their A/B split testing showed dramatically better response rates when they used “free” in the subject line, which caused them to conclude that “a free offer far outweighed the negative effective on clicks caused by triggering spam filters, resulting in a net click-through-rate gain.”
Since the article was written by a copy writer, I’d like to offer the perspective of someone with perhaps a more technical angle. As the eMarketing program manager, one of my job responsibilities is to ensure email deliverability of our email marketing application, which requires intimate knowledge of how spam filtering works on a technical level and how to avoid the spam filter for legitimate emails.
Our system sends over 30,000 emails per day, many of which contain blatant marketing terms that would surely trigger spam filters, yet we have an average delivery rate over 95%. Of course, like all email marketers, we cannot easily determine if the email was being delivered to the spam folder or the inbox, but we know from our server logs that the emails were accepted by the receiving mail server, and much of our own testing shows that we are getting emails into the inbox most of the time.
Based on my experience and testing, content-based solutions are losing prominence as the de facto standard for spam filtering. Anti-spam technology is advancing very rapidly and is moving away from content filtering because it doesn’t address the real problem and can never be as accurate as is required in today’s business environment where conducting business is done almost entirely by email.
Reputation-based solutions are supplanting content filters as the best way to suppress spam because it does address the root problem: bad senders. These newer solutions are extremely effective at blocking the real spam and allowing legitimate emails EVEN IF the emails content may seem suspect. Case in point: Lyris has a case study showing that even senders with risqué content, like Frederick’s of Hollywood, can achieve very favorable response rates if they adhere to email marketing practices that focus on ensuring that your recipients want to receive your emails.
You can be pretty sure that Frederick’s emails will be loaded with all kinds of words that would throw up red flags for any content-based anti-spam solution, but they still get high response because they adhere to email marketing best practices like making sure their list contains only opt-in recipients, writing great content, providing great offers, and purging their lists of complainers and non-responders.
You may be familiar with the “report spam” button that appears in the web interface for email providers like gmail, yahoo, and aol. This button is part of these newer reputation-based anti-spam solutions. When recipients click those “report spam” buttons, the email providers make note of the sender and keep track of how many people are complaining about that sender. Eventually, if enough people complain, the ISP or email provider simply stops accepting email from senders that receive a lot of complaints.
If your recipients are not complaining, the chances of your emails being tagged as spam are lower. Senders that consistently have a low complaint rate earn a degree of trust and are usually subject to less content filtering. This is a very efficient system because senders who use best practices, like only sending to opt-in recipients, purging their lists regularly, and writing great content, get rewarded with being subject to less filtering.
So, in the end, the use of “free” (or any other term) in the subject line, does not operate in a vacuum and is dependent on other factors as to its effectiveness. If you send any email to a list of recipients who have not agreed to receive emails from you and are not interested in what you have to say, then the chances are high that anything you put in the subject line will be ineffective. Conversely, if you build a relationship of trust with your recipients and they value what you have to say, then when you put “free” in the subject line, they will know it is legit, and they will open the email and respond to your offer.
