What do you think makes prospects open a sales email? A recognizable sender they trust? A tantalizing offer that captures their curiousity? Sheer habit?

How about none of the above?

At time in which companies are more concerned than ever about the efficacy of their email marketing (thanks to the advent of CASL in July), there’s a new research that reveals one very important element of successful electronic communication. According to a recent study from Toronto startup ContactMonkey—which provides tracking tools for sales emails—what really makes people open a message is a short subject line. As in, really short.

ContactMonkey analyzed more than 30 million emails sent by its clients in the past year in order to determine what makes for the perfect email subject line. The researchers found that the most-opened emails were those with subject lines of two words or less. On average, these messages had an 80% open rate. Furthermore, the typical recipient opened them more than twice.

What, exactly, those words should be is open to some debate. However, the general rule is that simple is best. Direct, clear words like “Update” or “Intro” yielded a 90% open rate, according to the researchers.

Read: The 5 Words That Make People Open Emails

Interestingly, the researchers found that the second-most-read emails had no subject lines at all, only a simple “Re:” or “Fwd:” in the subject window. (For a particularly killer combo, try “Re: Follow up,” a subject line that got 90% recipients to open the message.)

If it seems impossible to pare down your message, consider this: subject lines with five or more words were opened less than 15% of the time. The results are even worse when a message is vague; emails with the line “The results are in” yielded an abysmal 7.25% open rate.

This infographic details more of ContactMonkey’s findings:

What makes you open an email, sales or otherwise? Would you experiment with a shortened (or no-word) subject line? Share your thoughts by commenting below.

Read: 7 Keys to Killer Emails

Loading comments, please wait.