Check the address while the person can still fix it
Catch obvious mistakes at signup, allow for inconclusive checks, and confirm inbox access separately.
An email typo is easiest to fix while the person is still on your form. Later, you may have no way to reach them.
Start with basic format validation. Offer spelling suggestions where useful, but let the person choose. Then run any verification request from your server, where your API key stays private.
The response should change the form in a way that helps:
| Outcome | Form behaviour |
|---|---|
| Clear address error | Explain the issue and let the person edit it. |
| Positive result | Continue to the appropriate confirmation step. |
| Catch-all or other review flag | Avoid a blanket rejection; apply the rule that fits your product. |
| Inconclusive check or request timeout | Keep the address unconfirmed and provide a way to continue or retry. |
Don't leave a spinner running indefinitely. Keep the person's other answers so a failed check doesn't make them fill out the form again.
For a newsletter, confirmation can establish that someone with access to the inbox requested the subscription. For an account, require the appropriate ownership check before allowing actions that depend on that address. Letting a signup proceed during a timeout doesn't mean treating ownership as confirmed.
Show the submitted address on the confirmation page and make it editable. That also helps people whose mistake wasn't caught by verification.
Finally, keep handling bounces and address changes after signup. A check today doesn't ensure the address will still work next year.
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Keep a contact ID in your verification file
A simple export makes it easier to return each result to the right contact without exposing your whole CRM.
Before you connect an email verification API
Plan for unresolved checks, failed requests and changing addresses before putting verification into production.