The MessagePart property returns the current message part
index. All messages have at least one part, which consists of one or
more header fields, followed by the body of the message. The default
part, part 0, refers to the main message header and body. If the
message contains multiple parts (as with a message that contains one
or more attached files), the MessagePart property can be set
to refer to that specific part of the message.
Messages with file attachments typically consist of a message part
which describes the contents of the attachment, followed by the
attachment itself. For a message with one attached file, there would
be a total of three parts. Part 0 would refer to the main message
part, which contains the headers such as From, To, Subject, Date and
so on. For multipart messages, part 0 typically does not have a
message body, since any text is usually created as a separate part
(for those messages that do not contain multiple parts, the part 0
body contains the text message). Part 1 would contain the text
describing the attachment, and part 2 would contain the attachment
itself. If the attached file is binary, then the transfer encoding
type would usually be base64.