If you only need a restock email, compare apps on that job: a signup for the sold-out variant, and an email when stock returns. SMS, WhatsApp, and preorders are different requirements. They should not decide an email-only purchase.
The figures below are from the three App Store listings as shown on 16 October 2026. SK Back In Stock's listing shows a Free pricing line and does not state a monthly email cap. Stok's free plan lists 20 email notifications a month. SC Back in Stock's free plan lists 50 email alerts. Listings change, so open each one again before you choose. This article quotes only what those pages showed.
The email-only job
The shopper leaves an email on a variant that they cannot buy. You send one email when available quantity crosses a threshold you set. In SK Back In Stock the default threshold is 1. The inventory webhook does not send the mail itself. It queues a job. A worker uses your subject and body. Documented placeholders are product name, product URL, new price, and old price. A further increase, after the variant is already above the threshold, does not send another back-in-stock email.
If you need a text, WhatsApp, or a charge before the goods arrive, this email-only comparison is the wrong scorecard. Stok's paid plans list SMS and WhatsApp channels, and its plans include preorder offers. Ignore those extras while you are scoring email.
What each listing says
Each row comes from the public App Store listing as read on 16 October 2026. Prices are in USD and can change.
| App | Email on the listing, 16 October 2026 | Not stated on the listing |
|---|---|---|
| SK Back In Stock | Pricing shows Free. The listing says shoppers are notified by email when a sold-out product is back, with Notify Me through theme app blocks and size or color waitlists. | A monthly email cap, or any paid tier. |
| Stok | Free plan: 20 email notifications a month. Plus at $10 a month: 100 emails a month, with a per-email charge above that. Higher tiers list larger email allowances. | SMS or WhatsApp on the free plan. Those channels start on Plus. |
| SC Back in Stock | Free plan: 50 email alerts. Email Only plan at $10 a month: unlimited emails and a Klaviyo and Mailchimp mail-list sync. SMS is on the higher plans. | What happens after the 50th free email alert. WhatsApp is not mentioned. |
SC's Email Only plan is the one in this table that is priced around email. Its Klaviyo line is a mail-list sync. It is not a statement that you must use Klaviyo to send a restock email. If you do not use Klaviyo, compare the email allowance and the price, not the sync.
The SK limit the listing does not state
An email cap changes the buying decision as soon as the waitlist is larger than the cap. A store with a few sold-out sizes and a store that sells out a hero product every week do not have the same need. SK Back In Stock's listing shows Free pricing and does not print an email cap. That is not the same as a written promise of unlimited mail. Check the live listing and the app before you plan a large restock send.
Stok and SC do print their free allowances: 20 emails a month on Stok and 50 email alerts on SC. If your waitlist for one restock is bigger than that, look at the paid email tier on each listing. Stok lists a per-email charge above its paid allowances. SC's listing does not say what happens after alert 50. Do not assume overage, a hard stop, or an automatic upgrade.
Reviews and age are not in this comparison
No public review count, rating, or install age is quoted. Those figures change often, and they do not tell you whether an app sends the email you need. If popularity matters to you, read the figures on each live listing on the same day. Do not break a tie with a review figure you have not opened.
Neither age nor reviews replace a threshold test: join one sold-out variant with your own inbox, restock only that variant, and read the email. In SK Back In Stock the signup stores the variant, failed jobs retry up to five times, and recovered revenue sums later order lines that match the email and the same variant. Those checks do not tell you the monthly price.
What would change the recommendation
A recommendation depends on your own numbers. Before you choose, write down the following.
- The size of your largest waitlist for one restock, so you can compare it with each free allowance.
- SK's current pricing, and any cap shown on the live listing or inside the app.
- Stok's and SC's free allowance and paid email price, confirmed on the live listing the week you install.
- A yes or no, for your store, on SMS, WhatsApp, preorder, and Klaviyo. Extra features you will not use should not decide an email-only purchase unless they are the only way to get the email.
On 16 October 2026 the fair summary was this. SK documents a variant-level restock email and lists Free pricing without a stated cap. Stok's free plan lists 20 emails a month. SC's free plan lists 50 email alerts, and its $10 Email Only plan lists unlimited emails. If email is all you need, do not buy a channel you will not send.
Questions before you install
Is SK Back In Stock unlimited?
The listing does not say. It shows Free pricing and no email cap. Do not describe it as unlimited unless the listing or the app states it.
How many emails does Stok's free plan include?
Stok's listing showed 20 email notifications a month on the free plan on 16 October 2026. Check the live pricing table before you rely on it.
Should SMS be part of an email-only comparison?
No. If you will not text shoppers, score the email allowance, the variant signup, and the price you can actually see. Confirm SMS only when a text is the requirement.
Check the live pricing on SK Back In Stock before you treat it as the email-only choice.