`type t````=`

`|` `Auth of Email_address.t option`
`|` `Body of [ `Mime_8bit | `Mime_7bit ]`

``
`include sig ... end`
`val sexp_of_t : t ‑> Base.Sexp.t`
`val compare : t ‑> t ‑> int`
`val hash_fold_t : Base.Hash.state ‑> t ‑> Base.Hash.state`
`val hash : t ‑> Base.Hash.hash_value`
`val of_string : string ‑> t Core.Or_error.t`
`val to_string : t ‑> string`
`val list_of_string : allowed_extensions:Async_smtp_types.Smtp_extension.t list ‑> string ‑> t list Core.Or_error.t`
`module Stable : sig ... end`