5xx are bounces, a perm failure. 4xx error codes are temp (retry) errors.
Incorrect. A bounce is a delivery status notification generated by a mailer after it has already accepted a message for delivery. A 5xx permanent error is a refusal to accept the message in the first place.
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Incorrect. A bounce is a delivery status notification generated by a mailer after it has already accepted a message for delivery. A 5xx permanent error is a refusal to accept the message in the first place.