Getting your promotional email opened and read depends on a few key factors.
Making it mobile-friendly—including keeping the subject line concise—hovers near the top of the list. (We published previous guidelines here )
According to Campaign Monitor , about 53 percent of emails are opened on mobile devices. A study by Return Path found that open rates were 12.5 percent higher when subject lines contained fewer than 49 characters, though data were based largely on the retail industry.
Though Mailchimp states that the subject line length doesn’t actually matter , it recommends giving attention to length based on how email subject lines display on mobile devices. Zurb has a free tool for testing how subject lines display on popular mobile devices.