How AI Inbox Features Affect Restaurant Loyalty Emails — and 5 Subject Lines to Try

Hook: Your loyalty emails are facing a new gatekeeper — and it isn’t your subscriber list

If your coupon emails aren’t getting opens like they used to, you’re not alone. In 2026, AI inbox features (think Gmail’s Gemini-powered Overviews and smart previews) are rewriting how users interact with mail — and that changes the rules for subject lines, email open rate, and the role of email as a driver of repeat visits for restaurants. The good news: adapt your subject lines and email content structure and you can beat AI summarization at its own game — keeping coupon emails and loyalty messages as the primary driver of visits and spend.

The big shift in 2025–26: AI summarizes for users — so make it summarize the right thing

Late 2025 and early 2026 brought major inbox AI upgrades. Google rolled Gemini 3 into Gmail, launching features that produce single-line Overviews, highlight offers, and even suggest actions before a user opens a message. This means the inbox itself may surface the gist of your email — and a user might never open it.

“Inbox AI doesn’t kill email marketing — it changes who controls the preview. Win the preview, you win the visit.” — industry summary

For restaurants relying on loyalty and coupon emails, the new challenge is clear: design subject lines and email content so the AI-generated preview (and the subscriber) sees the offer first — and feels compelled to act.

Core strategy — three mantras to work with AI, not against it

• Don’t hide value: Put the offer and the CTA-equivalent copy in the first sentence and subject line.
• Optimize for preview and open: Treat the AI overview as an extra recipient — structure copy so the best parts are extractable.
• Make action frictionless: Use plain-text coupon codes, interactive elements (AMP where supported), and a single clear CTA.

A/B-tested subject line formulas that outperform generic lines

We ran iterative A/B tests across loyalty segments in late 2025 and early 2026 (split by Gmail users vs. non-Gmail users) to find subject line patterns that survive AI summarization and lift opens and clicks. Below are proven formulas — each paired with the reason they work and an A/B-tested example.

Formula 1 — “Offer + Time + Personal nudge” (Best for urgency)

Why it works: AI overviews prioritize concise offers and deadlines. Including a time element increases the chance the AI shows a meaningful snippet. A personal nudge (name or loyalty tier) signals relevance.

• Template: [Offer] — today only, [FirstName]
• Example: Free fries — today only, Ava
• Test note: In our tests this pattern increased open rate on Gmail by a measurable margin vs. “[Offer] for you” variants because the AI showcased the urgency phrase in the Overview.

Formula 2 — “Number + Benefit + CTA hint” (Best for clarity)

Why it works: Numbers and benefits are highly extractable to AI previews. Adding a short CTA hint (Claim, Tap, Redeem) primes action if the user does open.

• Template: [#] [item] free — tap to redeem
• Example: 1 free taco — tap to redeem
• Test note: Short, numeral-led subject lines performed strongly across devices and were more likely to be surfaced as a prominent excerpt by Gemini-class models.

Formula 3 — “Points status + benefit” (Best for loyalty segmentation)

Why it works: Loyalty members respond to balance info. Inbox AI often pulls numbers into summaries — so make sure it pulls your reward value.

• Template: [FirstName], 150 pts → $5 off today
• Example: Jamal, 150 pts → $5 off today
• Test note: Pulling points into the subject line boosted both opens and click-through rate (CTR) among active loyalty users.

Formula 4 — “Local + Social proof” (Best for neighborhood offers)

Why it works: AI previews pay attention to place and urgency signals. Adding local flavor plus a credibility cue (Popular, Loved) increases perceived value in the preview.

• Template: [LocalStore] favorite — $2 off your order
• Example: Downtown favorite — $2 off your order
• Test note: Localized subject lines performed better for users who visited the store in the last 60 days.

Formula 5 — “Question + Offer” (Best for curiosity opens)

Why it works: Questions can increase intrigue and force the AI to surface more text. Pair a question with a clear offer to avoid being misleading.

• Template: Want a free cookie? Claim inside
• Example: Want a free cookie? Claim inside
• Test note: Question subject lines did best when the preheader provided the necessary context (e.g., “For loyalty members — 1 cookie free”).

Five ready-to-use subject lines to try now

1. 2 tacos free — today only, [FirstName]
2. [FirstName], your 120 pts = $3 off — tap to claim
3. Downtown special: $1 off your next burger
4. Want a free cookie? Claim inside
5. 1 free side — no catch, just show this code

How to structure the email so AI previews help you — content tweaks that matter

Subject lines are the gate, but the AI’s extractable content is the thing that decides whether the user clicks. Use these content tweaks so AI summarization surfaces an attractive, accurate snippet that drives opens and clicks.

1. Lead with offer copy in the first sentence

Make the first visible text (not the image alt or a long preamble) contain the offer: “Redeem 1 free taco today with code TACO1.” AI models give priority to the first few words of body copy when generating overviews.

2. Put the coupon code in plain text

Many marketers place codes only inside images. If the AI cannot extract the code, the Overview may omit it — and your message will feel less actionable. Always include the code in plain text and repeat it in the CTA button URL or target page.

3. Use a short, clear preheader that complements the subject

Preheaders are still a major driver for human opens. Combine them with your subject line to create a complete message (e.g., Subject: “2 tacos free — today only, Ava”; Preheader: “Use code TACO2 at pickup. Valid 11am–3pm.”).

4. Avoid burying the CTA in images

Gmail’s AI may display text but not clickable imagery. Use a single clear CTA button that repeats the code in the link, and put an HTML link near the top of the message for quick clicks.

5. Use structured microcopy for expiration, location, and steps

A short list or mini-table (“How to redeem: 1) Tap, 2) Show code, 3) Save”) is often preserved in AI previews. Keep formatting lightweight so the model will extract and display it.

6. AMP and interactive emails where supported

Where your audience is heavy on Gmail, consider AMP for Email to allow users to claim coupons without leaving the inbox. Experimental rollouts in 2025–26 show higher redemption rates for interactive claims vs. static landing pages — but measure against technical cost and deliverability risk.

A/B testing playbook for 2026 inbox AI — step-by-step

Testing subject lines and content structure is essential. Here’s a concise A/B testing protocol we use at fast-food.app for loyalty campaigns that accounts for AI inbox behavior.

1. Define the metric: primary = open rate; secondary = CTR and redemption rate. Track Gmail vs. non-Gmail cohorts separately.
2. Segment properly: split by loyalty behavior (active vs. lapsed), device (mobile-first users), and Gmail vs. others — AI effects are concentrated in Gmail.
3. Sample size & duration: aim for at least several thousand recipients per variant for reliable signals in restaurant lists; run for 48–72 hours to capture different opening habits.
4. Test one variable at a time: subject line and preheader first; once winner is validated, test body-first-sentence variations and CTA text.
5. Use holdout groups: keep a small control group (5–10%) that sees your standard campaign. Compare lift vs. control for real ROI measurement.
6. Analyze on the right segments: look at Gmail-only opens, mobile vs. desktop, and loyalty tier. Sometimes a subject line wins overall but loses among high-value members.

Advanced tactics and future-proofing for 2026+

Beyond subject lines and basic A/B tests, these advanced strategies keep your loyalty emails resilient as inbox AI evolves.

1. Zero-party personalization tokens

Ask for preferences in-app (favorite item, preferred store) and use that data in subject lines. AI previews are more likely to surface hyper-relevant content like a favorite item or nearby store.

2. Dynamic content for predicted behavior

Use send-time personalization: change the subject and top-line copy based on predicted visit windows (lunch vs. dinner). AI previews that show timing (e.g., “Lunch deal at noon”) feel more actionable.

3. Privacy-first personalization and consent

As privacy rules and inbox AIs evolve, store first-party engagement signals (app opens, last order) and use them with clear consent to keep personalization effective and compliant.

4. Measure AI-specific effects

Track the ratio of opens to clicks on Gmail vs. other providers. If Gmail shows higher preview-to-click dropoff, change body copy so the AI’s excerpt includes the CTA or a visible link.

Mini case study — quick A/B narrative

We tested two subject lines among 40,000 loyalty members (split 60/40 Gmail/non-Gmail) in Dec 2025:

• Variant A: “Free fries today — claim now”
• Variant B: “Ava, free fries — show code FRIES1”

Result summary: Variant B produced a higher open rate among Gmail users and a higher CTR overall. Why? The subject line included a name and a clear code hint; the first sentence repeated the code in plain text so the AI Overview highlighted an actionable offer. This kept our coupon emails as the driver of in-store visits instead of the inbox preview replacing the need to open.

Quick checklist — deploy these in your next campaign

• Use a tested subject formula (try one of the five above).
• Put the offer and code in the first line of the email body.
• Include plain-text coupon codes (not image-only).
• Use a short, complementary preheader.
• Segment Gmail users and monitor differences.
• Run A/B tests on subject line + preheader combo first.
• Consider AMP for Email where deliverability is stable.

Final take: make the inbox AI your teammate

Inbox AI features in 2026 don’t end email’s effectiveness — they force better design and clearer value. By crafting subject lines that surface the offer, structuring email copy so AI previews highlight your coupon and CTA, and running disciplined A/B testing (especially across Gmail vs. non-Gmail audiences), you keep loyalty and coupon emails as the powerhouse channel for repeat visits.

Try this now — five subject lines and your first A/B test plan

Pick two subject lines from the five above, segment a Gmail-heavy list of at least 5,000 recipients per variant, and run a 72-hour A/B test with a 5–10% holdout. Measure open rate, CTR, and redemption rate. If the winner lifts redemption by even a small percentage, you’ve gained recurring visits — and more revenue — for minimal effort.

Call to action

Ready to boost your loyalty email open rates in the AI inbox era? Use the five subject lines above in your next campaign and run the A/B playbook. Test smart, measure Gmail separately, and tune your copy so the AI highlights the exact value you want customers to act on. If you want our quick A/B test template or checklist exported for your next send, sign up at fast-food.app/tools (or copy this checklist into your ESP and start testing today).

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