October 18, 2011
Case Study

Email Marketing: Back-in-stock alert emails achieve 22.45% conversion rate

SUMMARY: When a product is out of stock in your online store, there's a good chance customers will go elsewhere to find it, even just to check availability. How can you get these customers to return to your site when the item is back on your shelves?

Check out this online retailer's back-in-stock alert emails that achieve a massive 22.45% average conversion rate. Find out how they set up the program to ensure customers aren't burned twice.
by Adam T. Sutton, Senior Reporter


Online retail is a competitive market. If your product is out of stock, shoppers can easily check another store with a few clicks. This is exactly what Jim Moore, President, The PSNE Group, wanted to avoid at BirkenstockCentral.com.

BirkenstockCentral.com is an online-only shoe store owned by PSNE. It does not rely on drop shipping, and instead warehouses its products. Occasionally, the store runs short on certain styles, which can be problematic.

Moore needed to stop shoppers from abandoning his store when a shoe they wanted was out of stock. Rather than losing these customers to competitors, he needed a way to hold onto them.


The team created an out-of-stock email program, where shoppers looking for sold-out products could sign up to receive email alerts when the items returned. By making it easy to purchase from these emails, the team felt it could avoid losing customers.

Here are the steps taken:

Step #1. Automate out-of-stock notices

BirkenstockCentral.com offers a large number of products, many of which have multiple versions (such as different sizes of the same shoe). With such volume, the team needed to build an automated system to minimize heavy lifting for this program.

The team used an e-commerce system with real-time insight into the company's inventory. By working with developers, the team automatically updates product pages when an item runs out. Visitors to these pages would see:
  • Bold red text: "Temporarily out of stock"

  • Red-highlighted link: "Notify me when this size is in stock"

Step #2. Create lay-over form

After clicking the "notify me" link described above, visitors are presented a lay-over form with two options:
  • Commit to buy - customers can enter their purchase information and commit to buy the item when its back in stock. They will receive a notification approximately two days before the item ships, and are not charged until the item is sent.

  • Back-in-stock alert - customers can enter a name and email address to be notified via email when an item returns to the store. Customers using this option are not added to the team's general email marketing database.

BirkenstockCentral.com's system scans its inventory each evening to identify back-in-stock items and automatically sends alert emails to customers.

Step #3. Design a sales-ready alert email

The notification email BirkenstockCentral.com sends is primed for purchase. The message includes:
  • Large headline: "Back In Stock"

  • Personal greeting

  • Reminder of the customer's request

  • Product image and title of the correct product and size

  • Red "buy now" button

The button brings customers directly to an online shopping cart with the product pre-loaded into checkout. This approach removes a significant barrier to conversion by eliminating the need for customers to:
  • Visit a product page

  • Select a size

  • Add a product to the cart

  • Click "check out"

"There is not much else for them to do except pay for it at that point," Moore says.

Step #4. Realize products can sell out twice

The email also emphasizes that customers "not delay, as items are available in limited quantities." This is not just clever copywriting. Some products do sell out a second time before customers return.

The team is occasionally contacted by customers who received an alert email only to find the product sold out again. The company apologizes in such cases and offers to put customers back in the notification cue.

Always watch inventory

The team never sends more notifications than the number of products available, and the emails are delivered on a first-come, first-served basis.

"If we have five people waiting for the exact same item and we only get one in, we don't want to send out five emails and have four people be disappointed," Moore says.


"This is very important for us," Moore says. "The process has been more of a sale saver as opposed to a revenue generator."

The team's restock notification emails have great response rates. For a recent 30-day period they achieved:
  • Open rate: 36.5%

  • Read rate: 35% (defined as "open for at least five seconds")

  • Clickthrough rate: 26%

  • Conversion rate: 25%

The program has achieved a 22.45% conversion rate since its launch in March.

Not a sales driver

While the program's response rates are high, its sales volume is only a trickle compared to the rest of BirkenstockCentral.com's email marketing. Moore chalks this up to his team's effective inventory management.

The team does not want too many of these emails going out, Moore says, as it would reflect poorly on the company. Instead, these emails are sent occasionally and provide a service to customers that prevents them from shopping elsewhere.

Early-warning system

The program also alerts the team to missed opportunities. For example, if notification requests pile up for a particular product, the company is potentially losing revenue.

"We have a report that lists everything people are waiting for. So if we see 10 people waiting for the same size and color, then we have an issue. … That is a red flag and we take a look and investigate to see what the issue is and if it is something we can correct."

Multiple notices possible

The team may test a second alert email, delivered perhaps one week later if the customer does not respond to the first.

"We have done something similar with shopping cart abandonment and got some additional conversions there," Moore says.

Useful links related to this article

1. Out-of-stock product page
2. Notification form
3. Back-in-stock email

Remarketing Emails: How JetBlue's automated triggers get 1,640% more revenue-per-email than promotional emails

Email Marketing: Why Newegg's daily-deal alert emails garner a 60% average open rate

Remarketing Emails: 3-part triggered series generates 53% click-to-conversion rate

How to Build an SMS Alert Campaign: 6 Steps and Lessons Learned

Listrak - the team's email service provider


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