Kickbox

Kickbox has provided email verification since 2014 and is trusted by email service providers and brands. It verifies addresses in bulk and in real time, and checks syntax, domains, mail servers and mailboxes without sending an email.

Its signature feature is the Sendex score, a quality rating from 0 to 1 that goes beyond a simple valid or invalid verdict. An address can be technically deliverable yet still carry risk, for example because it sits on a catch-all domain or a new domain, and the score helps you decide how to treat those contacts. Results are grouped into deliverable, undeliverable, risky and unknown, and the real-time API can prompt people to fix typos as they enter their address.

Kickbox integrates natively with more than 25 email platforms, including HubSpot, ActiveCampaign, Klaviyo and Brevo, plus Zapier. It suits teams that want a mature, reliable verifier with a clear risk score for borderline contacts.

New accounts get 100 free verifications. Paid credits start at $5 for 500 verifications, scaling to $800 for 100,000 and $4,000 for one million, with custom quotes above that.