Preheader

A preheader is the short snippet of preview text that appears next to or just beneath an email's subject line in the inbox, before the recipient opens the message. Alongside the sender name and the subject line, it is one of the few pieces of information a person sees while deciding whether to open an email at all. Though small and easy to overlook, it functions as a second headline and can meaningfully influence open rates.

The mechanics depend on where the text is pulled from. By default, most email clients generate the preheader by grabbing the first readable text they find in the message body, which is often something unhelpful like a link that says view in browser or the opening words of a header. To avoid that, senders deliberately set a custom preheader, usually by placing a short, hidden line of text near the top of the email's code so the inbox displays it as the preview while it stays invisible inside the opened message. The amount of preheader text shown varies by device and email client, with mobile inboxes typically displaying less than desktop ones, so the most important words need to come first.

The name is a simple compound. "Pre" comes from the Latin for before, and "header" refers to the top matter of the message. The preheader is literally the text that appears before the reader opens the email and before the main content, sitting in the preview space of the inbox. The term became common as email marketers recognized that this preview area was valuable real estate they had been leaving to chance.

For a business, the preheader matters because it works in partnership with the subject line to earn the open, and the open is the gate everything else depends on. A subject line grabs attention, and a well-written preheader extends or completes the thought, adds a detail the subject omitted, or reinforces the value of opening. Used well, it turns a two-line pitch into a stronger case for attention. Left to default, it wastes that space on filler or, worse, displays awkward code text that makes the email look careless. Given how much competition crowds a modern inbox, that difference can move open rates in a measurable way.

The most common mistake is ignoring the preheader entirely and letting the inbox scrape whatever text it finds, which often produces a preview that undermines an otherwise polished email. Another error is simply repeating the subject line word for word, which squanders the chance to say something new; the two should complement each other rather than echo. A further nuance is front-loading the message, since truncation on small screens can cut off anything important placed too far in. Writing to the shortest likely display length is the safe approach. The preheader relates closely to the subject line, its partner in driving the open rate, and it is a natural candidate for A/B testing, since small changes to preview text can be measured against each other to learn what prompts a given audience to open.