Glossary
Email deliverability, defined
Twelve terms that decide whether a verification result means what you think it means. Each one cites its primary source and says what the verifier returns.
Catch-all domain
A catch-all domain accepts mail addressed to any local part, whether that mailbox exists or not.
Greylisting
Greylisting is an anti-spam technique in which a receiving mail server temporarily rejects mail from a sender it has not seen before, with a 4xx reply.
Role account
A role account is an email address that reaches a function rather than a named individual — info@, sales@, support@.
Unknown verification result
An unknown verification result means the mailbox was never tested — the probe was blocked, DNS failed, the server deferred, or the domain accepts every address.
Email list hygiene
Email list hygiene is the practice of keeping a mailing list free of addresses that no longer accept mail: removing hard bounces, honouring unsubscribes and complaints, and re-verifying before each send rather than finding out by sending..
Hard bounce
A hard bounce is a permanent delivery failure: the receiving server answered 5xx, usually because the mailbox does not exist.
Bounce rate
Bounce rate is the share of a send that the receiving servers refused: bounced divided by sent, as a percentage.
Spam trap
A spam trap is an email address that exists only to catch senders who mail people who never asked for it.
Disposable email address
A disposable email address is a temporary mailbox from a service that hands addresses to anyone, typically to get past a signup form.
MX record
An MX record is a DNS record naming the mail server that accepts email for a domain, with a priority number that orders the alternatives.
Email verification
Email verification asks the receiving mail server whether it would accept mail for an address, then stops before any message is sent.
Sender reputation
Sender reputation is the judgement a receiving provider forms about a sending IP and domain, from how recipients react to mail and how many addresses turn out not to exist.
Looking for a bounce code rather than a term? The SMTP reply code reference covers what each reply means and what the verifier returns when a server sends it.
Questions about verification
What is email verification?
Asking the receiving mail server whether it would accept mail for an address, and stopping before any message is sent. It confirms three things in order: that the address is well-formed, that the domain can receive mail, and that the specific mailbox exists.
What does the status value mean?
One of three things. Deliverable: the mail server confirmed this mailbox. Undeliverable: the mail server said it does not exist. Unknown: nothing was established, and the reason field says which of five conditions produced it.
What information does the email verifier provide?
The verdict, the reason code behind it, a sentence safe to show a customer, the three checks the verdict was built from, the actual SMTP code the server returned, the MX records, and flags for catch-all, disposable, role and free-provider addresses. No single opaque score — that was removed in favour of the evidence it stood in for.
What is the difference between email verification and email validation?
Validation is usually the local layers: is the address well-formed, and does the domain have a mail server. Verification is the network layer: does this mailbox exist, which only the receiving server can answer. Most tools use the terms interchangeably, so check what a given tool actually does.