Function build_with 

pub fn build_with(
    draft: &Draft,
    from: (&str, &str),
    tr: &Translator,
    date: i64,
    protection: Option<&mut Protection<'_>>,
    autocrypt: Option<&str>,
) -> Result<Outgoing, String>

The message as it goes out, protected when asked: PGP/MIME (RFC 3156), multipart/signed for a signature alone, multipart/encrypted otherwise, the signature then inside. autocrypt is your Autocrypt header’s value.