Why It Matters
Your subject line gets about 40-50 characters of visibility in most inboxes. The preheader gives you another 40-130 characters (depending on the email client and device) to make your case. That's a significant amount of extra real estate. Emails with optimized preheader text see measurably higher open rates compared to those that default to "View this email in your browser" or the first line of body content.
How It Works
There are two ways to set preheader text. Most email platforms have a dedicated preheader field in their editor. Under the hood, the preheader is typically a hidden <span> or <div> at the very top of the HTML body, styled to be invisible (zero font size, hidden overflow). Email clients scan the beginning of the body content to populate the preview area, so this hidden text gets picked up.
If you don't set a preheader, the email client will pull whatever text it finds first -- often navigation links, "View in browser" text, or alt text from images. That looks sloppy.
Quick Tips
- Write your preheader as a companion to the subject line, not a repetition of it -- they should work as a pair
- Keep it between 40-90 characters for the best cross-client display
- Add non-breaking spaces or zero-width characters after your preheader text to prevent the email client from pulling in body content