`include Async_smtp_types__.Envelope.Stable`
`module V1 = Async_smtp_types__.Envelope.Stable.V1`
`module V2 = Async_smtp_types__.Envelope.Stable.V2`
`module Sender = Async_smtp_types__.Sender.Stable`
`module Sender_argument = Async_smtp_types__.Sender_argument.Stable`
`module Id = Async_smtp_types__.Envelope_id.Stable`
`module Info = Async_smtp_types__.Envelope_info.Stable`
`module Retry_interval = Async_smtp_types__.Retry_interval.Stable`