Introduction

This article defines opt-in and opt-out checks and explains how Wunderkind determines a user’s email eligibility.

Email Eligibility Checks

For Wunderkind to evaluate a user’s eligibility for an email send, the program first confirms:

• It can identify the user via an email address.
• It can track an action on the site, such as an add-to-cart.

Note: Additional criteria beyond the items above may be required for send eligibility. This page focuses specifically on subscription status and how it determines opt-in/opt-out check status.

Once Wunderkind identifies both the user and the action on the brand’s website, the program determines send eligibility using either an opt-in check or an opt-out check, depending on the brand’s configuration.

What’s the difference between an Opt-In and an Opt-Out Check?

Opt-in status and opt-out status are explicit subscriber actions. Shoppers can actively opt in to brand marketing emails and they can actively opt out of a brand’s marketing emails, lists, and communications.

As long as a user has not actively opted out of the brand’s marketing list and messages, they are eligible under CAN-SPAM (US only) to receive behavioral emails from the brand. All emails must include an option to opt out to maintain compliance.

To summarize:

Opt-In check: A user is eligible to receive triggered emails only if they have explicitly subscribed (i.e., they exist as an active subscriber in the ESP). This is more common/required in stricter jurisdictions (e.g., regions that comply with GDPR and Canada’s CASL).

Opt-Out check: A user is eligible to receive triggered emails as long as they are not explicitly unsubscribed from the brand’s program. This is the norm for most US programs and aligns with CAN-SPAM when messages are transactional/behavioral in nature (e.g., cart/category/product abandonment).

Why is an opt out check critical to performance?

If a client runs an opt-in check vs. opt-out check (WKND best practice), the program may see a 15–50%+ decrease in send volume because it cannot send to all otherwise eligible users.  The actual impact varies by the specific opt-in mechanism:

• If Wunderkind runs a standard opt-in check against a comprehensive master subscriber list, the expected send volume impact typically falls around 15–25%.
• If Wunderkind runs a more conservative opt-in check against a narrower list (for example, subscribers explicitly opted into marketing emails only), the impact can be significantly higher. Depending on the discrepancy between the master list and the marketing opt-in list, send volume can decline by 50% or more.