How can I optimize the preheader?

The preheader is the line of text that shows up in the inbox right after your subject line. On mobile it might appear on the same line. On desktop it follows in a lighter color. Most readers glance at both before deciding whether to open. That gives you two short lines to make a case. Use them together.

The biggest mistake is letting your preheader default to "View in browser" or the first sentence of body copy. That's real estate thrown away. Set it intentionally, every time.

What works: let your subject line set up a question or promise, then let your preheader deliver the payoff or the specific. Subject: "Your June report is ready." Preheader: "Three things you should know before your next campaign." Subject and preheader working together gives you about 100-150 characters total. That's plenty to close the deal on the open if you use both purposefully.

Character count: aim for 40-100 characters for broad visibility across clients. Some clients show more, some show less. If your preheader is too short, the email body content can bleed in underneath it and look odd. Padding with whitespace or hidden zero-width characters stops that from happening, though it's a minor detail most readers never notice.

And don\'t repeat the subject line. It wastes the space. Don't use "This email contains..." or filler language. Write the preheader last, after you know what the email says. Subject line and preheader together form your first impression. Treat both with the same care, and then test combinations to see what your audience responds to. A/B testing subject-plus-preheader pairs is one of the highest-return tests you can run.