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Every validation request returns a classification, a deliverability score, and a set of signals that explain the result.

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Classifications

Relaybase classifies each email into one of three states:

Valid

The email passes the relevant validation checks and is considered likely deliverable.

Invalid

The email fails a fundamental validation check, or is rejected by the receiving mail server.

Risky

The email isn’t conclusively invalid, but Relaybase found something that means you should proceed with caution.

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Invalid

Common reasons an email is classified as invalid:
  • Invalid syntax
  • Domain without valid MX records
  • Disposable email domain
  • SMTP rejection from the receiving mail server

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Risky

Common reasons an email is classified as risky:
  • Catch-all domains
  • Greylisting from the receiving mail server
  • Role-based addresses (e.g. support@, admin@)
  • SMTP verification that couldn’t conclusively confirm the mailbox

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Deliverability score

Alongside the classification, Relaybase returns a score from 0–100: Relaybase calculates this deliverability confidence score using multiple signals, including email syntax, domain configuration, disposable-domain detection, role-based classification, provider characteristics, and SMTP verification when applicable.
The score is a confidence signal, not a guarantee of delivery. Even an email scoring 100 can’t guarantee that a message will actually be delivered — mailbox state can change after validation, and receiving servers can still reject a message at send time.
The score and the status classification are related but not derived from a fixed threshold — status is based on the underlying validation conditions, not simply “score above X equals valid.” Don’t build logic that assumes a specific score range maps to a specific status; always check the status field directly.

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Response fields

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Validation depth

You can control how thorough a single validation request is with the mode field: fast, medium, or deep. Lighter modes return faster; deeper modes run more thorough checks, including SMTP verification. See Validate an Email for how to set this on a request.