The inbox used to be a pretty straightforward place. Subject line at the top. Preheader tucked underneath. Open, read, click, repeat.
That's not the inbox anymore.
Since 2025 Gmail and Apple Mail have both rolled out AI-powered email summaries that now sit between your carefully written subject line and your actual email content.
Before a subscriber even opens your message, an algorithm has already read it, summarized it, and decided what it's really about.
That's a big deal, and most email marketers haven't caught up yet.
This guide breaks down how AI email summaries work in both Gmail and Apple Mail, what that means for your subject lines and preheaders, and exactly what to do about it.
Part 1: AI Email Summaries
What's actually happening in your subscribers' inboxes right now
Two of the world's biggest email clients have fundamentally changed how people read email.
Apple Mail (iOS 18.1+, macOS Sequoia 15.1+) introduced AI-generated message summaries as part of Apple Intelligence. Instead of showing the first line of your email as preview text, Apple Mail now shows an AI-written summary underneath your subject line automatically, without any action from the subscriber. There's also an on-demand "Summarize" button inside the email that generates a longer condensed version of the full message or thread.
Gmail entered what Google is calling its "Gemini era" in early 2026, integrating Gemini 3 AI throughout the inbox experience. Gmail's AI Overviews synthesize key points from email threads and surface action items. A new AI Inbox mode filters and prioritizes messages before users even see them.
The upshot: your email no longer speaks for itself in the inbox. An AI speaks for it first.
Gmail AI summaries: how they work
Gmail's AI summary features are powered by Gemini and work at the thread level. When a subscriber opens a long conversation, an AI Overview appears at the top that synthesizes key points across all replies. The AI also surfaces suggested action items, flags to-dos, and powers a natural-language inbox search ("show me emails from last month about my renewal").
A few things worth knowing for senders:
- Gemini reads the full email body, not just the first paragraph. That means burying your key message halfway down doesn't help you, the AI will find it regardless.
- Open rates may be inflated. Gmail's AI appears to auto-open emails to generate summaries, which means your open rate data is even less reliable than it was after Apple's Mail Privacy Protection rollout. Don't make decisions based on opens alone.
- Click-through rates are declining industry-wide. Emails with clear, front-loaded value propositions are maintaining significantly higher CTRs than those with buried CTAs, because subscribers who feel "informed" by the AI summary often don't click through for more. The gap between well-structured and poorly-structured emails is widening fast.
- Gmail's AI Inbox is still rolling out to broader audiences, but it actively filters, prioritizes, and groups messages. Sender reputation, engagement history, and content quality all influence how well your emails are treated in this new layer.
Apple Mail AI summaries: how they work
Apple's implementation is a little different, and in some ways more disruptive for marketers.
Inbox view: When Apple Intelligence is enabled, an AI-generated summary automatically replaces your preheader text in the inbox list view. A small grey icon indicates it's a summary rather than the original preview. The subscriber isn’t required to do anything to trigger it.
Inside the email: A "Summarize" button appears at the top of the email. Tapping it generates a short paragraph condensing the email's main points. For threads, it summarizes the entire conversation.
A few things marketers need to know:
- Your preheader text isn't gone, it's just not displayed as-is. The AI reads your preheader as input into the summary, but it won't show up verbatim. This means your careful subject + preheader pairings are effectively invisible to Apple Intelligence users.
- Image-heavy emails summarize poorly. Apple's AI can't read text baked into images. If your hero image contains your headline, your offer, or your CTA, none of that will appear in the summary. Only real, coded text gets picked up.
- ALT text doesn't help here. This one stings: testing has confirmed that Apple's AI does not use ALT text when generating summaries. So even if you've been conscientious about accessibility, it won't save your image-heavy email from a weak summary.
- Apple Intelligence hardware requirements limit who sees this. iPhone 15 Pro / Pro Max, any iPhone 16 model, iPads with M1+, and Macs with Apple Silicon running macOS Sequoia 15.1+ are required. Older devices still see standard preview text. That audience will grow every year.
- Users can turn it off. Settings → Apps → Mail → Summarize Message Previews. Some will. Most won't.
Gmail vs. Apple Mail: the key differences
| Gmail (Gemini AI) | Apple Mail (Apple Intelligence) | |
|---|---|---|
| Where it appears | Inside email thread (AI Overview) + AI Inbox tab | Inbox list view (auto) + inside email (on-demand) |
| Triggered by | Opening a thread / AI Inbox mode | Automatic in inbox; tap to summarize inside email |
| Reads images? | Partially | No |
| Reads ALT text? | Partially | No |
| Replaces preheader? | No | Yes |
| Can the user disable it? | Yes | Yes |
| Currently available | Rolling out broadly (2026) | iOS 18.1+, macOS Sequoia 15.1+ |
How to write emails that generate accurate, useful AI summaries
The good news: writing for AI summarization and writing for humans are not in conflict. The same principles that make an email clear and readable for people also make it easy for AI to understand and summarize well.
Lead with the most important information. Both Gmail and Apple Mail's AI tend to weigh the top of the email body heavily. If your key message, offer, or CTA is buried below a 200-word preamble, your summary will miss it.
Use real, coded text for everything that matters. Your headline. Your offer. Your discount code. Your CTA. If it's in an image, the AI won't see it. More on this in a moment.
Be specific, not clever. Teaser copy like "open for a surprise," mystery discounts, or emoji-only subject lines are kryptonite for AI summaries. The AI will do its best to explain what's in the email and produce a confused, vague summary. Save the mystery for the content; make the context explicit.
Accessibility matters: Use semantic structure. Headings, subheadings, and clear body text help both human readers and AI summarizers understand hierarchy. If your email has multiple sections, use text headings to label them. This is especially important for longer emails or newsletters.
Keep your CTA in text, not an image. A text button is readable by the AI; a button that's a PNG is not. This is good accessibility practice anyway, but now it's also good AI practice.
What to avoid if you want control over your summaries
- Image-only headers with key copy baked in. If your entire offer is in the hero image, the AI will summarize your email as if the offer doesn't exist.
- Long intros that bury the lead. "Hope this email finds you well. We've been working on something really exciting. You're going to love it." The AI will summarize this as: vague email with upcoming announcement. Not great.
- Multiple competing messages. The AI is trying to find the point of your email. If you have five equally weighted CTAs, the summary will be muddled. One email, one primary message.
- Relying on preheader text to complete your subject line (in Apple Mail). If your strategy depends on a subject + preheader pair that works together as a two-part joke or reveal, Apple Intelligence will break it. The preheader will be replaced by a summary of your email body.
Part 2: Putting It All Together
A framework for writing the full inbox experience
Think of your subscriber's inbox experience as three layers, each doing a different job:
- AI summary: tells the subscriber what the email contains. It's factual, not emotional. Your job here is to make sure the AI has clean, clear, specific text to work with so the summary is accurate and useful.
- Subject line: tells the subscriber why they should care. This is your emotional hook, your urgency, your relevance signal. It needs to stand alone.
- Preheader: extends the subject line for clients where it's still displayed, and gives the subject line more room to breathe.
Write them in that order. Start by asking: "If an AI read my email and wrote a two-sentence summary, what would I want it to say?" Make sure your email body actually contains the information to produce that summary. Then write a subject line that makes the reader care about what's in that summary. Then write a preheader that adds something the subject line didn't.
Before-you-send checklist
For AI summaries:
- ☐ Is the most important information in the first 100–200 characters of the email body?
- ☐ Are your headline, offer, and CTA in live text — not images?
- ☐ Is there one clear primary message, not five competing ones?
- ☐ Does the email use real headings and structured copy?
- ☐ Would you be happy if the AI summary was the only thing a subscriber read?
For subject lines:
- ☐ Does your subject line make sense without the preheader?
- ☐ Is it under 40 characters (or are the first 40 doing the heavy lifting)?
- ☐ Is it specific? Does it include a concrete benefit, offer, or reason to open?
- ☐ Did you avoid using the sender name (already visible in the inbox)?
For preheaders:
- ☐ Have you set a preheader? (Don't let the email client pick it for you.)
- ☐ Does it extend the subject line rather than repeat it?
- ☐ Is it under 90 characters?
- ☐ Does your subject + preheader pair still make sense for clients where both are visible?
