Definition
An inbox summary is a machine-generated short description of an email, displayed in the inbox list or preview pane. Gmail's Gemini, Outlook's Copilot and Apple Intelligence build these summaries from the subject line, preheader and opening lines of the email body.
The inbox summary is effectively the new first impression. For the last two decades, the subject line owned that job. Now a subscriber's decision to open — or not — is heavily influenced by a two-line AI summary they see before they ever tap the message.
What Determines the Summary
- Subject line — provides the headline context.
- Preheader / preview text — supplies the secondary hook.
- First two lines of the body — the primary source of summary content.
- Detected entities — dates, prices, links and names get pulled into the summary.
How to Control Your Inbox Summary
- Put the key fact or offer in the first sentence of the body.
- Use the preheader to reinforce, not repeat, the subject.
- Avoid long intros and pleasantries before the point.
- Keep a single, obvious call to action.
Related Terms
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
AI Content Detection
AI content detection refers to the growing ability of email clients, spam filters and consumers to identify machine-generated email copy. It matters for deliverability, trust and engagement in an era of mass-produced AI marketing email.
AI Email Summary
An AI email summary is a short, machine-generated overview of an email's key points, shown by Gmail, Outlook and Apple Mail before a recipient opens the message. It is reshaping how email marketers think about subject lines, preview text and open rates.
AI Inbox
An AI inbox is an email client that uses artificial intelligence to summarise, sort, prioritise and sometimes answer emails before the human recipient reads them. It is transforming email marketing metrics and copywriting.
Frequently Asked Questions
No. Preview text is the sender-supplied snippet shown in the inbox; an inbox summary is AI-generated from the email content. In AI inboxes, the generated summary often replaces the traditional preview text.
AI inboxes generate summaries from the email body rather than relying on the preheader field. If your summary looks generic, your opening lines are not carrying your value proposition.
Write the first two lines of your email as if they were a subject line — clear, specific and benefit-led — and give the AI a factual, structured message to summarise.