Constant EXPIRATION_HEADER 

pub const EXPIRATION_HEADER: &str = "amqp-expiration";

Header carrying the AMQP per-message expiration property of a DELIVERY: whole milliseconds, as decimal digits, which is how AMQP spells a TTL.

A delivery reports the property under this name. Publishing under it sets no property: the TTL of an outgoing message is LapinPublishSteps::expiration or the policy’s own LapinPublish::expiration.

The broker drops the message once the TTL has passed without it being consumed, dead-lettering it when the queue says so.