There's a piece of your email that most people see before opening it, and almost nobody writes on purpose. It's called the preheader (or preview text), and it's that second line that shows up next to or below the subject line in the inbox. If you've never set it, something's happening there anyway: the inbox fills it in on its own, usually with junk. And you're wasting the cheapest opportunity you have to lift your open rate.
This post is short on purpose, because the topic is too. But it's one of those five-minute fixes that pays off on every single send.
What it is, exactly
The preheader is the preview summary that email clients show alongside the subject line, before you open the message. On mobile it usually sits underneath; on desktop, to the right or below, depending on the client.
Here's the key part: if you don't set it yourself, the client generates it on its own, pulling the first words from your email's body. And what's usually sitting there? Things like "View this email in your browser," "Trouble viewing images?", or the alt text from your logo. In other words: your second-best shot at persuading someone, handed over to technical filler nobody cares about.
Look at the difference. An email with no preheader set looks like this in the inbox:
Subject: Your favorite cactus, 20% off through Sunday Preheader: View this email in your browser. Trouble viewing images?…
And the same email, with a preheader written on purpose:
Subject: Your favorite cactus, 20% off through Sunday Preheader: Plus free shipping if you add a planter. Through Sunday only.
The second one extends the promise of the subject line instead of throwing it away. It's double the space to say why opening is worth it.
How to write a good preheader
The golden rule: complement, don't repeat. The most common mistake is letting the preheader copy the opening of the body and end up saying almost the same thing as the subject line. That wastes the space twice over.
A few simple principles:
- Extend it, don't duplicate it. If the subject promises the discount, the preheader adds the detail that seals the deal (free shipping, a deadline, a second benefit).
- Make it stand on its own. Don't assume it'll always be read right next to the subject line — some clients cut it off or display it far away. It should make sense by itself.
- Lead with what matters. Just like the subject line, only the first characters show on mobile. Aim for roughly 40 to 90: put the good part up front.
- Watch out for "ghosts." Make sure "view in browser" or an image's alt text doesn't sneak in. If your first element is the logo, set an explicit preheader so it doesn't get hijacked.
Why it matters more in 2026
The same logic that applies to subject lines applies here. Major inboxes started using AI to summarize and prioritize the inbox (Gmail added a panel that summarizes emails; Nieman Lab, 2026). That automatic summary draws precisely on the subject line and the first lines of content — including the preheader.
Translation: a clear, specific preheader doesn't just persuade the person better; it also gives the AI better material to summarize you and rank you higher. A preheader full of "if you're having trouble viewing this email…" is a poor signal for both the human reader and the algorithm. The invisible text stopped being invisible: now both of them read it.
How arrobaMail handles it
In the arrobaMail editor you have a dedicated field for the preheader, separate from the body, so you're not at the mercy of whatever the inbox decides to grab. And when you build the campaign with Amanda IA, it proposes the preheader alongside the subject line, designed as a pair: one makes the promise, the other seals it. You choose and fine-tune.
It's not the biggest lever in your email marketing, but it's one of the cheapest: five minutes per campaign, and every send makes the most of space you used to give away for free.
Want to try it on your next campaign? Create a free account and see the difference between a preheader written on purpose and one left to chance. And if you haven't yet read about its partner in crime, check out how to write subject lines that get opened.