The preheader, also called preview text, is the short line shown after or below the subject line in most inboxes. Gmail, Apple Mail, Outlook and mobile apps all display some of it, so it is effectively a second subject line. If you don’t set one, the mail app takes the first text it finds in the email, which is often “View this email in your browser” or an image’s alt text.
A good preheader adds to the subject rather than repeating it. If the subject says “Our monsoon sale starts today”, the preheader might say “Raincoats, umbrellas and boots from ₹499, until Sunday”. Together they give the reader enough to decide whether to open. The preheader is also a good place for the detail that wouldn’t fit in a short subject line: a deadline, a price or the main benefit.
How much is shown depends on the app and the screen. On phones, roughly 40 to 90 characters are typically visible after the subject; on desktop it can be more, depending on the length of the subject itself. Put the important words first and treat anything after about 90 characters as a bonus.
Common mistakes include leaving it blank, repeating the subject word for word, and writing something that contradicts the email. A misleading preheader can also feed complaints, just like a misleading subject line. Test preheaders along with subject lines when you run A/B tests, since the two work as a pair.
A Jaipur stationery brand writes the subject “Back-to-school kits are here” and the preheader “Everything for Classes 1 to 5 in one box, delivered in 2 days”. Before, its emails showed “Having trouble viewing this email? Click here” as the preview.
Every MailNesto campaign and automation email has its own preview-text field, and subject-line A/B tests can give each version its own preview text.