SmtpMessagePart.HeaderData is not all headers

[KoromaruKoruko]

I am writing unit tests to verify a mail client.

SmtpMessagePart.HeaderData only contains the value of Content-Type. For my tests I need to verify attachments and linked resources(inline attachments). I am unable to differentiate between the two nor any other kind of mime part as I can't get the value of Content-Disposition.

Please include a way to get the full set of headers for a mime part.