How to verify an email address without sending one

Syntax and domain checks

First, the address is checked for valid format and obvious typos. Then its domain is checked for MX records — if there are none, the domain can't receive mail and anything there will bounce.

Mailbox-level probing

A verifier opens a conversation with the receiving mail server, as a sender would, to learn whether the specific mailbox would accept a message — then stops before actually delivering anything. No email is ever sent.

Why not just send a test?

• Test sends to bad addresses still count as bounces.
• They can hit spam traps and hurt your reputation.
• They're slow and don't scale to a whole list.

What you can't always know

Catch-all domains accept everything, so a specific mailbox can't be confirmed from outside — those come back as catch-all rather than valid or invalid, and are best treated as risky.