The email subject line and preheader are two elements the recipient sees before opening the message, and they determine the open rate. The preheader is a short text shown in the preview right after the subject line, and most companies leave it unfilled, so the template's opening phrase or the link to view in a browser gets pulled into it instead. Write the subject line short, because long text gets cut off in a mobile inbox, and specific – factual information works better than a mysterious phrasing, which stops working entirely after the first disappointment. Avoid words and punctuation typical of spam, capital letters and excessive emoji. Use the preheader to add to the subject line, not to repeat it. Test subject lines, but always on a sufficient sample.
See also: Email Deliverability, Statistical significance of a test, Unsubscribe and complaint rate.
