Definition
Email verification
Checking before you send whether an address exists and can receive mail, so bad addresses never reach a campaign.
Email verification is a set of checks run on an address before any message goes out. Is it well formed? Does the domain exist and publish mail servers? Does the mail server say the mailbox exists? Is it a role address or a disposable one? Each check narrows the list of addresses that will bounce, and the outcome is usually labelled valid, invalid or unknown.
It matters because a bounce is not a neutral event. Every hard bounce is a mark against your domain, and a list with many dead addresses can push a campaign over the point at which providers start filtering everything you send. Verification turns that risk into a decision you make before sending, when it costs nothing. The honest limit is the catch-all domain, where the server accepts every address and verification cannot say more than unknown.
In Seegnals verification runs on import, including catch-all detection, and a catch-all result is reported as unknown rather than dressed up as valid. Addresses that cannot be verified are held in the To check queue before the first send, where you fix or skip them. Duplicates and addresses already on your suppression list are caught at the same step.