The subject line should link seamlessly to your main headline and then to the lead copy and into the body of the email. Ensure that the subject line is relevant to the content and incites a relevant expectation – clickbait is bad, folks! Open rates are not the only metrics by which to measure success (I’ve heard it said that open rates are ‘vanity’ and clickthroughs are ‘sanity’).
When it comes to deciding how to craft that perfect subject line, there appears to be really only one area to avoid: the subject line of 60 to 70 characters. Marketers refer to this as the “dead zone” of subject length. According to research by Adestra, which tracked over 900 million emails for its report, there is no increase in either open rate or clickthroughs at this 60-to-70 character length of subject line.