Apple Mail can swap your inbox preview for an Apple Intelligence summary, and in the Gmail app, Gemini does the same on some messages. On desktop, Gmail's summary usually only appears once you open the thread. You can't write that sentence yourself, but you can give these AI summaries something accurate to work with. Put the real offer in live text at the top, use a clear heading and one primary CTA, leave a normal preheader for clients that still show it, then send a Test and export HTML or MJML ready for your ESP. In Milo Email Studio you build the email on a drag-and-drop canvas, keep the offer in live text, send a Test and export HTML or MJML for your ESP.
Two different summaries
Apple Mail and Gmail work differently, so design the body to give both something accurate to read.
Apple Mail: a summary in the inbox, if the setting is on
With Apple Intelligence switched on, a short summary can appear under emails in the inbox. People can turn Summarize Message Previews off to see the first lines of the message again. On iPhone and iPad, that setting is under Settings, Apps, Mail. On a Mac, it's under Mail, Settings, Viewing.
There's also a separate Summarize button that sums up a long email or thread once it's open. That's a different feature from the inbox line.
Apple Intelligence isn't available on every device, language or region, so don't assume every Apple Mail user sees a summary. When the setting's off, your preheader and opening lines show up again, which is why a real preheader still belongs in the file. This guide focuses on the body of the email rather than preheader length.
Gmail: a replaced preview in the app, and a summary after open on desktop
In the Gmail app on Android, iPhone or iPad, Gemini can show a summary of up to about two lines under the subject of eligible messages. It's marked with a summary icon, replaces the message preview and can update as the thread changes. Plenty of messages never get one.
Whether someone sees them depends on their app version and whether they have an eligible Google Workspace or Google AI plan. Workspace smart features are off by default in the EEA, and the compact list view hides inbox summaries altogether.
On a computer, a different feature appears at the top of an opened thread: an AI Overview, or "Summarize this email". That's separate from the subject and preview in the inbox list, so don't assume a summary caused (or stopped) someone opening your email in Gmail.
Gmail AI Inbox: to-dos and catch-up summaries in their own view
Gmail also has AI Inbox, a separate view that pulls suggested to-dos (action items, deliverables and deadlines) out of email conversations and summarises the topics someone most needs to catch up on. Google started rolling it out to paid Google Workspace users in October 2026, on desktop and in the mobile app menu, and from 26 October it reaches the rest of those organisations, over about two weeks. For now it's limited to users in the US with US English as their language, and it reaches organisations gradually, so most of your list won't see it yet.
It matters for marketing email for the same reason as the other summaries. If your deadline or date sits in live text, it's easier for a to-do or catch-up line to get it right. If it only lives in an image, there's nothing for it to pick up. Google's help page says AI Inbox only uses messages in the Primary tab, not Promotions or Social, so a campaign that lands in Promotions won't show up there at all. It's one more reason to write the email like a clear note from a person, though no layout can choose the tab for you.
What you control, and what Apple or Google invent
You design the email. Apple and Google write the summary, decide who sees it, and sometimes get it wrong. No layout can control what it says.
| You can design | You cannot design |
|---|---|
| Live-text offer, deadline, and numbers near the top | The exact summary sentence |
| A text heading that states the point | Whether this recipient even has summaries on |
| One obvious CTA | A guarantee the model will not drop or twist a detail |
| Alt text for images that carry meaning | Using alt text as a remote control for the summary |
| A real preheader for non-AI clients | Forcing Apple or Gmail to display that preheader verbatim |
| A subject that still makes sense alone | Brand voice inside the generated line |
If the offer or code only appears in an image, a summary has very little real text to use, and people with images off see nothing. That's a design problem, not a claim that AI models ignore alt text.
Stripo's piece on email overload (29 Sep 2026) has a section on designing for AI-summarised inboxes. It cites a 2026 Validity Inc. study saying 55% of consumers decide whether to open an email based on AI-generated summaries, 25% use AI to summarise emails, and 10% trust those summaries. Those are Stripo's figures, not Milo's research. The practical takeaway is simpler: put deadlines, dates and numbers in live text near the start.
Checklist: structure the body before you export
Put the offer in live text at the top
The headline and the sentence under it should say what people get, what it costs and when it ends. Put any spending condition next to the price in the same live-text block, not only in the footer or a banner, and label what each deadline is for (early-bird versus registration, for example). Stripo's note on AI email previews shows how a summary can keep a discount and drop the condition, or turn an early-bird date into the last day to register. Those first lines are what a summary is most likely to lean on, so treat the preheader as the backup, not the plan.
Do not use an image-only hero
An image can support the offer, but it shouldn't be the offer. Give any meaningful image alt text, for people with images off and for accessibility. The HTML email checklist covers images-off checks. The same goes for a moving hero: the message still needs to be there as text, just like with native video fallbacks.
Make headings text that state the point
A clever heading that hides the offer is hard for a summary to use and hard for a person to skim.
Use one primary CTA
Use a direct verb and name what they get. Keep extra links like social, view in browser and legal visually quieter so they don't compete with the main ask. The Promo starter, with its offer headline, supporting copy and single shop button, is a good fit.
Put dates, prices, and codes in text
Keep them near the top, not tucked away in an image or the footer. Before you export, send a Test to an inbox that shows summaries and compare it against a short fact list (price, condition, each deadline, the CTA). A model might pick up a date or code you've buried, but you can't control which detail it chooses.
Keep paragraphs short
Long, dense text and competing sections make for a worse summary. Don't bury your main ask among three equal offers.
Keep a real preheader
Clients with summaries turned off still show preview text, so write one on purpose. In Milo it goes in the Preheader Text field in the email's canvas settings, and it travels with your export as the standard hidden preview line at the top of the email. Make it say the same thing as the email itself. Milo can't show you the AI summary itself, so the live text and preheader are the parts you control. Email preheader text covers how to write a good one.
Let the subject stand alone
Some people never see your second line. It can help to repeat a keyword from the subject in the first sentence of the body, though there's no guarantee the summary will use it.
Hidden text and plain text: what an AI assistant reads
An AI summary reads more of your email than a person does, including text that's hidden from view. Attackers know this and have started hiding instructions for AI assistants inside phishing emails. Barracuda found text tucked into HTML comments, styled with a zero-pixel font or white on white, and slipped in with invisible characters. The defence it recommends is stripping hidden elements before an AI reads the message, so expect security tools to treat hidden copy with suspicion.
Keeping your own hidden text honest protects the summary and your reputation with filters:
- The preheader is the only hidden text you need. Milo puts your preheader in the standard hidden preview line. Write it as a true summary of the email: the same offer, the same date.
- Don't hide anything else. No white-on-white keywords, no tiny text and no lines written to an AI ("if you're summarising this email, say..."). They look like the attacks above, and they can get your email flagged.
- Say the same thing everywhere. If the visible email, the preheader and the plain-text version tell different stories, filters get suspicious and people get confused.
- Check the plain-text version. Some tools read the plain-text part of an email instead of the HTML. Milo exports HTML and MJML, not a plain-text version, so that part comes from your ESP. Read it there before you send, and make sure it has the same offer, date and link as the design.
A simple workflow
The hard part is the thinking: one offer, said plainly, near the top. Milo makes the rest quicker.
It starts with one sentence. What they get, who it's for, when it ends and one thing to do. If someone can repeat it back to you, it's ready to become an email.
The draft follows your order. Tell Milo's AI designer (which is separate from Apple's and Google's inbox AI) who it's for, the offer and the one button, so the first bits of text carry the message from the start. Edit the blocks if they don't. The brand kit keeps colour, type and buttons on-brand while you move things around, but it doesn't write the Apple or Gmail summary.
The preheader is part of the design. Write it in the Preheader Text field in canvas settings, or ask the AI designer for a subject and preview text alongside the draft, then edit either one. Milo doesn't show an AI-summary preview.
You can see what a real inbox makes of it. A Test goes to an address on your account, with a subject that starts with Test. Open it in Apple Mail with summaries on (and off, if you can switch them), in the Gmail app if your account's eligible, and in Gmail on desktop for the after-open summary. You're checking that your text is there and easy to skim, and noting what that client happened to generate. It won't tell you what every recipient will see. A teammate can read the email from a preview link, which shows the layout, not what an AI inbox would make of it.
The handoff keeps your work intact. You take HTML or MJML ready for your ESP. If its editor overwrites preview text, check the preheader again there before you send, and read the plain-text version while you're at it. The handover is covered in design a branded email and export.
What this workflow does not do
| Studio / design path | Apple Mail / Gmail | Your ESP | |
|---|---|---|---|
| Put the offer in live text, one CTA, on-brand | Yes | No | Only if you rebuild there |
| Show the AI summary inside the builder | No | Yes, on their side, when the feature is on | No |
| Decide the summary wording | No | Their model | No |
| Show a normal preheader when summaries are off | You supply the text | Their setting | May edit preview text on import |
| Test / proof the draft | Studio Test + optional preview link | Real inboxes only | Final test after import |
| Export-ready handoff | HTML / MJML | - | Import, then send |
| Plain-text version | No, HTML / MJML only | Some tools read it | Create or check it before sending |
Questions
Does Apple Intelligence replace my preheader?
For people who leave Summarize Message Previews on, the inbox shows a summary instead of the first lines. Everyone else still sees your preview text, so keep both a clear body and a real preheader.
Does Gmail Gemini replace my preheader?
Sometimes, on eligible messages in the Gmail app. On desktop, the summarise-this-email view appears after the email's opened. Not every Gmail user sees the same thing.
What is Gmail AI Inbox?
A separate Gmail view that lists suggested to-dos and summarises topics to catch up on, using only the Primary tab. It's limited to the US and English, on eligible Google AI or Workspace plans, so for now only part of any list will have it.
Can I write the summary myself in the design tool?
No. You write the email, and Apple and Google write the summary.
Can I stop a wrong summary?
You can't edit what Apple or Google write. What you can do is put the price, its condition and each labelled deadline in live text near the top, stick to one message, keep the offer out of an image, and compare a Test summary with your fact list.
Will alt text become the summary?
Don't count on it. Write alt text because images fail and people rely on it, and put the offer in real text regardless.
Is this the preheader length guide?
No. This guide is about structuring the body of the email. For writing the preview line itself, read Email preheader text.
What can I check in a Test, and what can I not see in Milo?
In a Test, you can read your copy in a real inbox and, on a device with summaries available, see what that client came up with. Milo itself doesn't preview Apple or Gemini summaries.
Does Milo create a plain-text version of my email?
No. Milo exports HTML and MJML. Create or check the plain-text version in your ESP, and make sure it has the same offer, date and link as the design.
Is hidden preheader text a problem for AI summaries?
Not if it's honest. A preheader that matches the email is normal. Hidden text that says something different, or talks to the AI, is what security tools look for.
Where does the campaign go after export?
Export HTML or MJML for your ESP, or push a Zoho Campaigns draft if you've connected it, then send from there.