Back to Glossary
Email Structure

Subject Line

The headline of an email that appears in the inbox, crucial for determining whether recipients open the message.

Definition

The subject line is the title of an email that recipients see in their inbox. It is the primary factor in open decisions and appears alongside the sender name and preheader. Effective subject lines grab attention, communicate value, and encourage opens while accurately representing the email content.

Why It Matters

Subject lines directly determine whether your emails get opened. With crowded inboxes, you have seconds to catch attention. A great email with a poor subject line will not get read. Subject line optimization is one of the highest-impact improvements you can make.

How It Works

Subject lines are set when composing an email and appear in the recipient's inbox. Length varies by email client; mobile typically shows 30-40 characters while desktop shows more. Certain words, characters, and patterns can trigger spam filters.

Best Practices

  • 1Keep subject lines concise (30-50 characters for mobile visibility)
  • 2Front-load important words since text may be cut off
  • 3Test different approaches: questions, numbers, personalization, curiosity
  • 4Accurately represent the email content to build trust

Frequently Asked Questions

There is no perfect length, but aim for 30-50 characters to ensure visibility on mobile. Put the most important words first. Longer subject lines can work if the beginning is compelling.

Emojis can increase visibility and convey emotion, but use them sparingly and appropriately for your brand. Test with your audience - some respond well, others find them unprofessional.