Configure a Mailjet API-key pair and authenticated sender

Mailjet sending uses an API-key/secret pair and validated senders. Record which account or subaccount owns the pair before connecting production; an identically named domain in another context does not make credentials interchangeable.

Prepare the account context

1. Add the application sender/domain and complete the current verification/authentication instructions.
2. Select the intended account/API-key context and store both halves of the pair in the backend secret manager.
3. Confirm which sending endpoint/version your integration uses. Send API v3.1 has a Messages array and a different contract from older examples.
4. Separate sandbox validation from an approved live test and document the production From identity.

Consult Mailjet’s developer docs for the required request fields and sender activation. Do not infer inbound DNS from outgoing domain authentication.

Verify without widening permissions

First validate message structure using the documented sandbox mode where appropriate. Then explicitly authorize a live send to an inbox you control; sandbox success is not proof of delivery.

For an authentication error, check the exact key pair and account context. For a sender error, inspect sender verification. Do not expose either credential in a screenshot or copy the secret into a public API example.

If MailKite receives replies while Mailjet sends, document which address routes to each service. The same From domain does not create shared message IDs, route configuration, or suppression state.