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email.sender_not_validated

Recorded as an outbox message's lastErrorCode: Mailjet refused the send because the partner's sender is not validated; the row is Failed and the sender becomes Unverified.

Codeemail.sender_not_validated
HTTP statusNone: a result code, recorded on a resource (for example an operation's resultCode) rather than returned as a problem response (— (result code))
ArgumentsNone (args is {})

Handling it

Branch on code, not on title or the status alone, and log traceId. Codes are stable; new codes may appear, so fall back on the HTTP status for a code you do not know. See Handling errors and the list of codes.