Catch-all domains

A catch-all (or "accept-all") domain is configured to accept email sent to any address at that domain — even ones that don't have a real mailbox. Send to anything@example.com and the server will say "accepted" regardless.

Companies use catch-all configurations for different reasons: to avoid losing emails sent to misspelled addresses, to route all mail through a central inbox, or simply as a legacy default they never changed.

Catch-all domains are the hardest addresses to verify. When MailSentry asks the mail server "does john@example.com exist?", the server says "yes" — but it says the same thing for asdfghjkl@example.com. There's no way to distinguish real mailboxes from non-existent ones through SMTP alone.

This is why catch-all results show verification_level: "inferred" instead of "confirmed". Since SMTP can't help, MailSentry analyses the local part — name patterns, bigram quality, separator structure, and digit ratios — to estimate how likely the address is to belong to a real person. The result is a variable penalty instead of a flat one.

It depends on the local part. Instead of applying a flat penalty to all catch-all addresses, MailSentry scores them based on how likely the local part is to be a real person:

• Name patterns like john.smith@ or j.doe@ receive a small penalty (-5 to -10) — these are very likely real people.
• Single natural-looking words like michael@ get a moderate penalty (-10 to -15).
• Ambiguous or short locals like a@ or x1@ get a higher penalty (-20 to -30).
• Gibberish or numeric-heavy locals like xq7z@ or 12345678@ get the heaviest penalty (-30 to -35), stacking with gibberish detection.

This means john.smith@catchall-domain.com can still score 95 (valid), while xq7z@catchall-domain.com drops to risky or invalid — even though SMTP treats them identically.

• Trust the score, not just the catch-all flag. MailSentry already factors local part quality into the score. A catch-all address scoring 90+ is likely safe to send. One scoring below 60 is not.
• Don't block them outright. Many legitimate businesses use catch-all configurations. Blocking them would reject valid customers.
• Segment by score for large lists. If you're cleaning a B2B list, sort catch-all addresses by score. Send to 80+ immediately, monitor 60–79 in a separate batch, and suppress anything below 60.