Few emails are as welcome as the one that says the thing you wanted is back. The shopper found a product, wanted it enough to hand over an email address and was told to wait. That is a more specific signal than a cart, a browse or a newsletter sign-up, and yet many stores either do not offer the option at all or handle it with a generic plugin they never revisit.
This guide covers the whole loop: where to capture requests, what to store, how to trigger the email safely, what to write, how to avoid sending ten thousand alerts for fifty units, and how to measure the result. It sits alongside the other flows in our flow best-practice guide and shares an inventory dependency with low-stock alerts and reorder points, which is where restocks start.
Why back-in-stock emails work
A shopper who joins a restock list has done three things: chosen a product, accepted that it is unavailable and given you permission to contact them about it. Most email flows start with a guess about intent. This one starts with a statement of it. That does not guarantee a purchase, since prices, needs and patience change, but it is a reason the flow tends to be among the more productive in a store, and it is cheap to run because the audience builds itself.
There is a second benefit that is easy to miss. The list is a free demand signal. If two hundred people ask for a size that you sold out of last week, that is evidence for your next purchase order. We cover how to use that signal in demand forecasting for small stores.
Capture the request
The sign-up lives on the product page, in place of the add-to-cart button when the selected variant is unavailable. Keep it to the minimum: an email field, a clear label and a short line saying what will happen. If you also collect a phone number for text alerts, make consent explicit and separate, and follow the rules that apply in your market; see our ecommerce SMS marketing guide.
| Field | Why you need it | Common mistake |
|---|---|---|
| Where the alert goes | No consent wording near the button | |
| Product and variant ID | So the alert names the exact size or colour | Storing only the product, so the alert is vague |
| Date and source | To send in order and to measure demand | No timestamp, so order is lost |
| Consent record | To show what the person agreed to | Adding them to the general newsletter by default |
| Status | Waiting, sent, purchased or expired | No status, so people get repeat alerts |
Do not silently subscribe a notify-me request to your marketing list. The person asked for one thing. Send that one thing, and offer the newsletter as a separate, optional choice if you wish. It protects deliverability as well as trust.
Trigger the email from a verified change
The trigger should be an increase in available inventory for that variant, from zero or below a threshold to a quantity you are confident about. The risky versions of this flow are the ones that fire on a product edit, a tag change or a draft being republished, because they send before there is anything to sell.
- The inventory system records that variant X went from 0 to 40 available.
- The automation checks that the product is active, published and purchasable.
- It counts the waiting requests for that variant and takes the oldest first.
- It sends up to a chosen multiple of the available units, so that the list is not larger than stock.
- It marks those requests as sent and records the time.
- It stops when the variant sells out again, and resumes at the next restock.
Sending to everyone at once when you have received a small batch produces a bad experience: the first twenty buy, and the other four hundred click through to a sold-out page. The multiple depends on your conversion rate on past alerts. If one in six alerted shoppers buys, sending three alerts per available unit is a sensible starting point. Adjust from your own data.
Timing
Send soon after the stock is confirmed. A shopper who asked a month ago may have bought elsewhere, so there is no benefit in waiting for a convenient time of day. For long gaps, add a freshness check: if a request is more than a few months old, either ask whether they still want it or send once and then retire the request. Avoid sending alerts overnight in the recipient’s time zone when you can.
| Situation | Suggested handling |
|---|---|
| Large restock | Send to everyone waiting, in order, over a short window |
| Small restock | Send to a limited number in order, with a note that stock is limited |
| Request older than several months | Send once, then expire the request |
| Variant sells out within hours | Stop sending, keep remaining requests waiting |
| Discontinued product | Tell people and suggest an alternative once, then close the requests |
Write the email
The message has one job: get the shopper to the right variant of the right product while it is still available. A product image, a clear subject, the variant, the price and a button are enough. Add a single line of urgency only if it is true.
| Element | Example | Note |
|---|---|---|
| Subject | Back in stock: Linen Tablecloth, Natural, 140 x 220 cm | Name the exact item; avoid vague “good news” lines |
| Preview text | You asked us to tell you. Limited quantity. | Only say limited if it is |
| Headline | It is back | Short |
| Body | The size you wanted is available again. We have a small number, so this link goes to your exact variant. | One or two sentences |
| Button | Buy now | Links to the variant with the variant selected |
| Footer | You received this because you asked to be notified. We will not email you about this item again. | Sets expectations and supports trust |
Examples of subject lines
- Direct: “Back in stock: Ceramic Mug, Matte Green”
- Personal: “The size you wanted is back”
- Limited, if true: “Back in stock, with a small quantity”
- With a variant: “Medium is back: Hooded Rain Jacket, Navy”
- With a nudge: “It is back, and it may go again quickly”
Avoid subject lines that claim urgency you cannot prove. If you say “only five left” and there are 400, the next alert from you gets less attention and may attract complaints. Honest and specific outperforms clever over time.
Handle the awkward cases
- Variant returns at a different price. Show the current price. If it is higher, say nothing misleading about it being the same.
- The shopper bought elsewhere on your store meanwhile. Suppress the alert if the same customer already ordered that variant.
- Pre-order stock. If the item returns as a pre-order, say so clearly with the dispatch date. See backorder and preorder management.
- Multiple variants waiting. Send one email per variant, not one per request, and group them if two arrive together.
- Bundles. Alert when every component is available, not when one is.
- Overselling. Reserve stock for alerted shoppers only if you can do it reliably; otherwise cap sends. Our inventory sync guide explains why numbers drift between channels.
Build it on Shopify or WooCommerce
There are three ways to build the flow. Use an app with a notify-me form and built-in sending, store the requests in your email platform and trigger from an inventory event, or build the capture and trigger yourself using inventory webhooks. App-based setups are quick, but check how they handle limits, variant-level requests and the order of sends. A custom flow gives control over the cap and the suppression rules. For the event side of things, see Shopify webhooks explained.
| Approach | Strengths | Limits |
|---|---|---|
| Dedicated app | Fast, form and sending included | Less control over caps, ordering and suppression |
| Email platform flow | Reuses your templates and reporting | Needs a reliable inventory trigger and variant data |
| Custom automation | Full control, any channel | Needs building and monitoring |
Whichever you pick, test it with a product you control. Mark a variant as sold out, submit a request, restock it with a small quantity and confirm that one email arrives with the right link. Then test a restock while the product is a draft, and a restock to a quantity of zero. Our AI back-in-stock alerts service and email and SMS flows service cover this build.
Measure what matters
| Metric | How to read it |
|---|---|
| Sign-up rate | Requests divided by views of sold-out variants. A low rate may mean the form is hidden. |
| Alerts sent | Should track available units, not list size. |
| Click rate | Shows interest; compare with other flows. |
| Alert-to-order rate | The key number; it guides the send multiple. |
| Revenue per alert | Orders from alert links divided by alerts sent. |
| Complaints and unsubscribes | A rise suggests stale or repeated alerts. |
A worked example
A store sells a popular jacket and sells out of medium for three weeks. During that time 310 shoppers request an alert. A supplier delivers 60 units. Using a past alert-to-order rate of about one in five, the store sends 180 alerts in sign-up order, three per unit. Of those, 41 shoppers buy within two days, and the remaining stock sells to ordinary traffic. At a $120 average order, that is about $4,900 from a single restock, with no discounts, and 130 requests remain waiting for the next delivery. Compare that with sending all 310 at once: the same 60 units would sell, but 250 shoppers would meet a sold-out page. The figures are illustrative and use a rate you should replace with your own.
A checklist before you switch it on
- The form appears only when the selected variant is unavailable.
- Requests store the variant, timestamp and consent.
- The trigger is a verified inventory increase on an active, purchasable product.
- Sends are capped relative to units available and ordered by sign-up time.
- Alerted customers who already bought are suppressed.
- The email links to the exact variant and shows the current price.
- Requests expire after a defined period.
- A weekly report shows sign-ups, sends, orders and revenue.
Sources and further reading
Figures and rules in this guide come from the primary pages below. Platform limits and prices change, so open the page before you build on a number.
- Shopify Help Center: inventory, how inventory quantities are tracked by variant
- Klaviyo Help Center: back in stock, how back-in-stock alerts and flows are set up
- FTC: CAN-SPAM Act compliance guide, requirements for commercial email