How accurate is email verification, really?
No verifier can promise 100% certainty on every address — and any that claims to should make you suspicious. Here's what verification gets right, where the limits are, and how to read the results honestly.
What it nails
Syntax errors, typos, non-existent domains and domains with no MX records are caught reliably — these are clearly invalid and will bounce. So are most disposable and role-based addresses.
Where certainty ends
Catch-all domains accept everything, so a specific mailbox can't be confirmed from outside. Some servers also greylist or time out, producing an unknown result. Honest verifiers report these as catch-all or unknown rather than guessing.
How to read a quality score
A per-list quality score blends all these signals so you can judge a whole list at a glance. A high score means most addresses are clearly valid; a lower one flags more risk to investigate before you send.
Accuracy is also about honesty
The most useful verifier is the one that tells you the truth about uncertainty — flagging catch-all and unknown clearly — rather than inflating a valid count to look better.