Marketing software platform Hubspot performed a very interesting test recently regarding the use of the word "Free" in email.
The purpose was to determine what impact the word had on email deliverability and click-through rate. HubSpot set up an A/B email test - one with free in the subject line and one without.
The results may surprise you.
As related to deliverability, the word "free" on its own will not hurt your emails' deliverability according to Hubspot but it may raise some red flags with "carrier grade" filtering solutions, those used by some big ISPs (reason enough in my opinion to leave the word well enough alone).
In relation to click-through rate however, the use of the word "free" tells marketers a much different story. The email without the word free in the subject line performed 17 percent better. Another reason to pass on using the word "free" in both subject lines and the body copy of emails.