The optimum length for an email subject line is a topic of much controversy. A wide variety of variables affects how your subject line displays in any given instance: what email reader the recipient is using, whether they’re using a preview pane, and what type of device they’re reading your email on.
Indeed, the exponential growth of smartphones is putting increased pressure on marketers to shorten their subject lines. According to eDialog, 34% of all consumers now check their email on a mobile device at least once per day. If that mobile device is a smartphone, only about five words of the subject line will be visible.
That doesn’t mean you must truncate all your subject lines right away. Plenty of subscribers will still see more than the first five words. But more and more readers will only see the beginning of your subject line, so be sure to frontload it with your most important message in the first few words.