How Do I Limit Back-in-stock Notifications to the First 100 Customers on a Waitlist?
Why You Would Cap the Send at All
You cap a back-in-stock send because emailing 400 people about 60 units guarantees that 340 of them have a bad experience. The cap protects the customer relationship and your email reputation at the same time.
There is a second reason that gets less attention. An uncapped blast destroys your ability to learn anything. When 400 emails go out and 60 units sell, you cannot tell whether the alert converted well or whether the inventory simply ran out. A capped send gives you a clean measurement, because the number of people who could buy and the number of people who were asked to buy are close to each other.
The cap also protects deliverability. Mailbox providers watch engagement. A send where most recipients click through to a dead end and then stop opening your messages teaches the provider that your mail is less wanted. Over enough restocks that reputation cost is real.
For merchants on OpoShop, the practical framing is simple. A back-in-stock email is a promise. Only make it to as many people as you can keep it for.
How a Capped Send Works Under the Hood
A capped send is an ordered query with a limit, executed at the moment inventory becomes available. Every part of that sentence matters.
The mechanism has four pieces:
- Ordering: Requests sort by the timestamp they were created, oldest first, so the queue is chronological and defensible.
- Scope: The query is filtered to one variant, so a size run does not blend into a single list.
- Limit: Only the first N unnotified requests are selected for this send.
- State change: Each selected request is marked as notified, so the next send picks up where this one stopped.
That last piece is where homemade solutions usually break. If a request is not marked after it is emailed, the next restock re-selects the same first 100 people and positions 101 through 400 never hear from you at all. Mark first, then send, and treat the mark as the record of who has been contacted.
A worked example makes the ordering concrete. A variant has 380 requests. You restock and cap at 100. Requests 1 through 100 are marked and emailed. Two days later you restock again and cap at 100 again. This time the query skips the marked rows and selects requests 101 through 200. The queue advances instead of repeating.
Restockly handles this bookkeeping automatically, which matters because the failure mode is silent. Nothing errors. The same hundred people just keep getting emails while the rest of your OpoShop waitlist waits forever.
How to Set Up a Capped Notification
The setup is short once the queue is stored properly. Most of the work is deciding the number and confirming the ordering is right.
Those five steps cover the mechanism. The parts worth thinking about are below.
1. Apply the cap per variant, not per product
A cap of 100 on a product with twelve variants is almost meaningless. If the medium black restocks, the cap should apply to the medium black list, not to a blended list across every size.
Per-variant caps also keep the math honest. You restocked 40 mediums, so you cap the medium list. The large list is untouched because no larges arrived. Blending the lists sends alerts to people whose size is still gone.
2. Mark first, send second
Email delivery can fail, retry, or partially complete. If your process sends first and marks afterwards, a failure halfway through leaves half the batch marked and half not, and the recovery run double-emails people.
Marking first means the worst case is that a few people are marked but never receive the email. That is a much better failure than the same shopper getting three identical alerts, and it is easy to detect and repair.
3. Decide what happens to positions 101 and beyond
The people you did not email are the whole point of the cap, so decide their treatment deliberately. They should keep their original timestamp, stay unnotified, and sit at the front of the next send.
Some stores also send this group a short queued message that names their approximate position. It sets expectations without promising anything. Test it before making it standard, because on some OpoShop catalogs it increases anticipation and on others it just adds an email nobody asked for.
Hard Cap vs Rolling Batches vs Inventory-Matched Cap
There are three ways to limit a send, and they suit different inventory situations.
| Method | How the limit is set | Best for | Watch-out |
|---|---|---|---|
| Hard cap | A fixed number such as 100, every time | Predictable restocks of similar size | The number is arbitrary and often wrong for the actual delivery |
| Rolling batches | Fixed batch size sent repeatedly until stock clears | Most stores and most restocks | Needs an automatic stop when inventory hits zero |
| Inventory-matched cap | Cap calculated from units restocked and conversion rate | Scarce or high-value products | Requires a reliable conversion figure to calculate from |
A hard cap is the easiest to explain and the easiest to get wrong. One hundred is a fine number if you routinely restock 40 to 60 units. It is a poor number if this delivery was five units or five hundred.
Rolling batches are the best general answer. You set a batch size, the system sends the first slice, waits, checks stock, and sends the next slice only if units remain. That handles a five-unit restock and a five-hundred-unit restock with the same configuration.
An inventory-matched cap is the most precise. If you restocked 60 units and your alerts convert at 35 percent, the calculation points to roughly 170 emails to clear the stock. That precision is worth having on expensive products where each unit represents meaningful revenue. Most OpoShop stores get there by starting with rolling batches and tightening the number once they have their own conversion data.
Choosing the Right Number Instead of Guessing 100
The right cap is the number of emails that will sell roughly the number of units you have, which means it depends on two figures you can measure.
The first is available units. Not incoming units, not units on a purchase order, but stock a shopper can add to cart right now.
The second is your alert conversion rate, meaning the percentage of alerted shoppers who complete a purchase. Restock alerts convert far better than ordinary marketing email because the recipient asked for the message, so expect a much higher figure than your newsletter.
Divide units by conversion rate and you have your cap. Sixty units at a 40 percent conversion rate points to about 150 emails. Sixty units at 20 percent points to about 300.
Two adjustments are worth making. Round down when the product is scarce and disappointment is expensive, because a slightly slow sell-through beats a wave of frustrated shoppers. And round up when the restock is large and aging inventory is the bigger risk. On an OpoShop storefront selling seasonal goods, sitting stock costs more than a slightly oversized send.
What to Do With Everyone Below the Cap
The customers below the cap are still customers, and how you treat them decides whether the waitlist survives more than one restock cycle.
Keep four things true for them. Their signup timestamp does not change. Their unnotified status does not change. They move to the front of the next send. And they can leave the list at any time with one click.
Beyond the mechanics, there is a communication choice. You can stay silent until their turn arrives, or you can send a short note that they are in the queue at roughly position 140. Silence is safer and perfectly acceptable. A position note works well for hyped drops where anticipation is part of the appeal.
What you should never do is quietly drop them. A shopper who signed up months ago, never heard anything, and later sees the product back in stock without an email will conclude that the list does not work. That single impression costs you every future signup from that person.
It is also worth reviewing the tail of the list occasionally. Requests older than several months on a product you no longer plan to restock should be closed out with an honest email pointing to a current alternative. A clean queue is more useful than a long one.
What We Recommend for [OpoShop](https://oposhop.io) Merchants
We recommend rolling batches sized from your own conversion rate, applied per variant, with marking before sending and an automatic stop at zero stock.
Start with a batch of 100 if you have no data yet, because it is a reasonable middle for a typical restock. Send it, watch how many units clear, and calculate your real conversion rate from that single send. After two restocks you will have a number specific to your store, and you should use that number instead of the default.
Then check three behaviors before your next drop. Does the second batch select different people than the first? Does the send stop when stock is gone? Do the people below the cap keep their original position? Those three checks catch nearly every capped-send bug on an OpoShop store.
The cap is not a limitation on your marketing. It is what makes the waitlist trustworthy enough that people keep joining it.
Best answer: Sort the waitlist by signup time, filter to the specific variant, mark the first 100 requests as notified, then email only that slice and leave the rest queued at their original positions. Better still, derive the number from units restocked divided by your alert conversion rate, so each send in your OpoShop store matches the stock you actually have.
If you want a waitlist that stays orderly across every restock, start with the platform your store already runs on.
FAQs
Should the cap apply to each variant or to the whole product?
To each variant. A restock of 40 mediums should only trigger alerts on the medium waitlist. Applying a product-wide cap emails shoppers whose size is still unavailable and wastes most of the send.
How do I make sure the next batch reaches different people?
Mark each request as notified at the moment it is selected, and have the next send skip marked rows. Without that flag, every send re-selects the same people at the front of the queue.
Is 100 a good default cap?
It is a reasonable starting point for a typical restock of a few dozen units. Once you have one send of data, replace it with units divided by your measured alert conversion rate, which will be specific to your store.
Should I tell customers below the cap where they are in line?
It is optional. A short queued message with an approximate position builds anticipation on hyped products. Staying silent until their turn is equally valid and adds no extra email.
What if the first 100 do not buy the stock?
Send the next batch after a few hours. Rolling batches exist for exactly this reason. Keep sending slices until inventory clears or the list runs out, whichever happens first.
Does capping hurt total revenue from a restock?
No, as long as you keep sending batches until stock clears. The units sell either way. Capping changes who has a good experience, not how many units move.
Ready to run restocks that feel orderly instead of chaotic? Start with the store platform behind it.
