Some domains are configured as "catch-all"—they accept email sent to any address, even if that specific mailbox doesn't exist. This complicates email validation because the server will report every address as "valid."
What Are Catch-All Domains?
A catch-all configuration routes all unmatched emails to a default mailbox. For example, sending to [email protected] might be accepted and forwarded to [email protected]. Small businesses often use this to avoid missing emails sent to guessed addresses. However, it means you can't verify individual mailboxes exist.
Detecting Catch-All Domains
Validation APIs detect catch-all by testing random, invalid-looking addresses. If the server accepts obvious nonsense like [email protected], the domain is flagged as catch-all. Once detected, individual addresses can't be verified with certainty. APIs will return "unknown" deliverability for these addresses.
How to Handle Catch-All in Your App
For signups, you may accept catch-all addresses but flag them as "risky." For marketing lists, consider a double opt-in (send confirmation email) to verify the address actually works. Avoid removing catch-all addresses entirely—many are legitimate business emails. Instead, segregate them for closer monitoring of engagement metrics.