Genuinely effective campaigns segment the market as carefully as possible, and target accordingly. Relevancy is key for getting people to open emails and respond to your CTA – but what's ‘relevant' differs from person to person. If you're going to make your emails as relevant as possible to everyone who reads them, you need to Segment, Target, and Position.
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.