How to Write Better Subject Lines (According to Data)

Every successful cold email starts with a good subject line. The first thing the person sees when your email lands in their inbox, it’s also one of the main criteria they will consider before opening it.

But what makes a cold email subject line effective?

To figure this out, we’ve dusted off our lab coats and analyzed 712k first-step emails with unique subject lines.

Get data-backed insights on the key subject line parameters


Does the length of your subject line have an impact on the open rates? How long should it be to drive maximum results?

Letter case

Could the letter case used in your subject line really influence the open rate? Is it better to  capitalize it or use lower case?


Does adding personalization variables to a subject line help generate higher open rates? How many variables should you use?


Should you add emojis to the subject line? How do they influence the open and reply rates of your cold emails?