How do validation tools use SMTP pings?

**SMTP** pings connect to recipient mail servers and initiate delivery without completing it. The server's response indicates whether the address exists. Accept responses suggest valid; reject responses indicate invalid. The connection closes before actual delivery.

Process: connect to MX server, identify as sender, specify recipient address, observe response code, disconnect. Valid addresses typically get 250 (accepted) responses; invalid get 550 (user unknown) or similar rejections.

Limitations: some servers accept all addresses during **SMTP** then bounce later, some implement tarpitting delaying responses, some rate-limit connections affecting bulk validation, and privacy-focused servers may not confirm existence. **SMTP** pinging is useful but not foolproof.