Function deferred_props 

pub fn deferred_props(envelope: &Envelope) -> BasicProperties

AMQP properties for publishing envelope into a hold queue.

Identical to props_for with no delay, and that is the point: a deferred message must not carry an expiration. The wait is the hold queue’s queue-wide x-message-ttl; a per-message expiration on top of it would reintroduce exactly the mixed-TTL head-of-line blocking that hold queues exist to avoid, and a shorter one would release the job early.