Definition
The subject line is the primary text in the From line area that appears first, and it is the single biggest driver of whether someone opens an email. The preheader is the shorter preview snippet of text that appears next to the subject line in the inbox.
In many clients the preheader defaults to the first body text, which is often wasted. A well-crafted preheader complements the subject line rather than repeating it, adding context, value or a call to action to tip the open decision.
Treat them as a team. The subject grabs attention and the preheader seals the deal by adding one more piece of compelling information. Both should be tested as part of your open-rate strategy.
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Frequently Asked Questions
The subject line is the main teaser that drives opens; the preheader is the short preview text beside it that adds context and reinforces what the email is about.
Email clients auto-fill the preheader from your body text when no custom preheader is set. Add an intentional preheader to control the preview and strengthen your message.
The subject line grabs attention and the preheader reinforces it by adding context, value or a call to action. They should complement, not repeat, each other.