Mailster Kickbox adds real-time Kickbox email verification and email validation to the Mailster Newsletter Plugin for WordPress. When someone subscribes, the address is checked through the Kickbox API before it is saved—so invalid, disposable, and low-quality emails stay out of your list.

Cleaner lists mean fewer hard bounces, stronger sender reputation, and better email deliverability for your Mailster campaigns.

This plugin requires Mailster 4.0 or newer and a Kickbox account with an API key. Subscriber email addresses are sent to Kickbox for verification.

Why use Kickbox email verification with Mailster?

Real-time verification on signup — Kickbox validates the address as soon as someone subscribes through Mailster (forms, admin, and other flows that use Mailster’s subscriber verification).
Fewer bounces — Undeliverable and rejected addresses are blocked before they hurt your reputation.
Disposable, role, free & catch-all filtering — Optionally reject trashmail domains, role accounts (e.g. info@, support@), free providers, or accept-all (catch-all) domains.
Sendex quality score — Set a minimum Kickbox Sendex threshold so only higher-quality addresses are accepted.
Rules you control — Accept or reject based on Kickbox results (deliverable, risky, unknown, undeliverable) and detailed reason codes.
Custom error messages — Show clear feedback when an email is not accepted.
Configurable timeout — Adjust how long Kickbox may take to respond (milliseconds).
Credit balance in settings — See remaining Kickbox verification credits from the Mailster settings screen.
Optional import checks — Enable verification during bulk import, or keep imports fast and verify large lists in Kickbox first.

How it works

Install and activate Mailster Kickbox alongside Mailster.
Enter your Kickbox API key under Newsletter Settings Kickbox.
Adjust acceptance rules if you need stricter or looser filtering.
New subscribers are verified automatically via the Kickbox Verify API.

Learn more about verification results in the Kickbox API documentation and result terminology. Addon overview: Use Kickbox with Mailster.

Additional Info

This plugin requires the Mailster Newsletter Plugin for WordPress 4.0 or newer and an account at Kickbox. Subscriber emails are verified via the Kickbox API.