`type t`````
`include sig ... end`
`val sexp_of_t : t ‑> Base.Sexp.t`
`val create : ?⁠from:[ `Keep | `Change_to of Email_address.t ] ‑> ?⁠to_:[ `Keep | `Change_to of Email_address.t list ] ‑> ?⁠cc:[ `Keep | `Change_to of Email_address.t list ] ‑> ?⁠subject:[ `Keep | `Prepend of string ] ‑> Email_message__.Email_simple.Content.t ‑> t`
`val create_from_email : Email_message.Email.t ‑> t`
`val add : t ‑> Email_message.Email.t ‑> Email_message.Email.t`
`module Stable : sig ... end`