What Is a Preheader?
When a subscriber views their inbox on a mobile phone or desktop email client, they see three pieces of information before opening any message: the sender name, the subject line, and the preheader. The preheader is that brief text snippet, typically 40 to 90 characters, that previews what is inside the email. In Gmail on Android, for example, it appears in grey text directly beside or below the subject line.
Technically, the preheader text is inserted into the email's HTML, either as a visible element styled to match the email background colour (making it invisible once the email is opened) or as a dedicated preheader field provided by your email service provider. If no preheader is deliberately set, most email clients will pull the first readable text from the email body, which often produces awkward or unhelpful preview text like "View this email in your browser" or empty alt attributes from images.
The preheader is one of the most neglected elements in email marketing, yet it has a direct impact on open rates. Research consistently shows that emails with a relevant, well-crafted preheader outperform those that rely on the subject line alone. For South African marketers sending campaigns to opted-in lists, optimising the preheader is a quick, low-effort change that compounds across every send.
Preheader In Practice
A Durban-based travel agency sending a promotional email might use a subject line like "Long weekend deals: Cape Town from R1,200" paired with a preheader that reads "Book by Friday and save an extra 10% on flights and accommodation." The subject line captures attention and states the offer, while the preheader adds urgency and a specific incentive. Together they tell the whole story before the subscriber decides whether to open.
Avoid repeating the subject line verbatim in the preheader. This wastes valuable preview space and signals lazy copy to subscribers. Instead, treat the preheader as a second sentence that expands on the subject. If the subject creates curiosity, the preheader can tease the answer. If the subject makes an offer, the preheader can reinforce the benefit or add a deadline. Keep it concise, keep it relevant, and always test two preheader variants as part of your regular A/B testing practice to learn what resonates with your specific audience.
How email preheaders work
A preheader is the short preview text that appears alongside or just after the subject line in an email inbox, giving recipients a further glimpse of the email's content before they open it. Most email clients display this preview text next to or below the subject line, pulling it from the start of the email or from a preheader you specifically set, so it acts as a second line of persuasion working with the subject line to earn the open. Because inbox space shows the sender, subject line and preheader together, the preheader is valuable real estate: a well-crafted one extends and complements the subject line, adding information or enticement that increases the likelihood of an open, while a neglected preheader wastes the opportunity, often showing stray text, such as a "view in browser" link or the opening words of the email, that does nothing to encourage opening. Setting the preheader deliberately means you control this preview and use it to strengthen the case for opening the email.
Writing an effective preheader
An effective preheader works with the subject line rather than repeating it, adding a complementary detail, benefit or enticement that together make a stronger case to open than either alone. It should be concise, since only a limited amount shows before it is truncated (the visible length varies by email client and device, so front-load the important words), and it should be relevant and honest, matching what the email delivers, since a misleading preview wins an open but loses trust. Treating the subject line and preheader as a pair, one hooking, the other reinforcing or extending, gets more from the combined inbox preview than a subject line alone. Always setting the preheader deliberately, rather than leaving it to default to stray text, ensures the preview supports the open. Because small improvements to what shows in the inbox can lift open rates, and open rates gate everything downstream, the preheader is a small but worthwhile element to craft, testing it alongside subject lines to see what encourages opens for your audience.
FAQ
How long should a preheader be?
A preheader should ideally be between 40 and 90 characters. Shorter preheaders risk showing filler text pulled from the email body, while longer ones get truncated on mobile devices. Aim for a single compelling sentence that extends the subject line rather than repeating it.
What happens if you do not set a preheader?
If no preheader is set, most email clients automatically pull the first readable text from the email body. This often means recipients see generic filler phrases like 'View this email in your browser' or alt text from an image, which reduces open rates significantly compared to a deliberately crafted preheader.