How it works

1. Syntax: the address is parsed and malformed input is rejected.

2. Domain: the domain’s mail servers (MX records) are looked up. No mail server means invalid.

3. Mailbox: where the receiving server allows it, the server is asked whether it would accept the recipient. No message is sent.

4. Signals: disposable domains, role mailboxes and free providers are flagged.

Timeouts, greylisting, provider errors and servers that do not answer mailbox questions lead to unknown. Unknown results are not billed and carry a retryable field.

Catch-all domains accept every recipient, so the mailbox cannot be confirmed and the result is catchall. Large mail providers may restrict mailbox checks.

• Product overview
• Verification results
• Verification reasons