Email verification 101: valid, invalid, catch-all and unknown
Run a list through any verifier and you'll get back statuses like valid, invalid, catch-all and unknown. Here's what each one means and what to do with it.
Valid
The mailbox exists and can receive email. These are safe to send to. In a healthy list, most contacts should land here.
Invalid
The address doesn't exist, the domain is wrong, or there's a syntax error or typo (like gmial.com). These will hard-bounce — remove them before you send.
Catch-all (accept-all)
The domain accepts mail for any address, so the verifier can't confirm the specific mailbox exists. These are risky: some are real, some aren't. Send to them cautiously, or only to your most engaged segments.
Unknown
The mail server didn't give a clear answer (greylisting, timeouts). A good tool retries; persistent unknowns are best left out of important sends.
What a quality score adds
A single 0–100 score blends these signals so you can judge a whole list at a glance. BounceBlock returns a quality score plus the per-contact breakdown, so you know exactly what you're working with before you pay.