Module `Async_smtp__Message.On_disk`

module Metadata : sig ... end with type t = t: Spoolable.Metadata.t should be smallish since it is read and written more frequently than Spoolable.Data.t.

module Data = Data: Spoolable.Data.t is where the "real" data lives and it allows for data-specific load and save functionality.

module Queue = Queue: Queue.t is an enumerable type that represents the available queues and the mapping to directory names on-disk.

module Name_generator : Async_smtp__.Multispool_intf.Name_generator.S with type t = Async_smtp_types.Smtp_envelope.t and module Unique_name = Id

module Throttle : sig ... end: All operations that touch disk are passed through Throttle.enqueue