Why can't my SMTP tool validate the Risky Emails?

SMTP (Simple Mail Transfer Protocol) verification works by performing a "handshake" with the receiving mail server to check if an email address exists. Here's the technical process:

1. Your tool connects to the recipient's mail server
2. It says "I want to send an email to [email protected]"
3. The server responds with either acceptance or rejection

With catch-all domains, the server is configured to accept ALL incoming connections, regardless of whether the specific mailbox exists. This means:

• Every address returns a "valid" handshake response
• The tool cannot distinguish real addresses from fake ones
• Results are marked as "Accept-All" or "Risky" — not valid or invalid

This is why tools like ZeroBounce, NeverBounce, and MillionVerifier cannot give you a definitive answer for these addresses.

Scrubby takes a different approach: instead of relying on SMTP handshakes, we perform actual inbox-level testing over 48-72 hours, monitoring what happens when a test email is sent. This gives definitive valid/invalid results that SMTP-based tools simply cannot achieve.