PlainText property will return part of the message that
has content-type of text/plain. It
could be whole message, but also any of its parts.
wodMailbox will search through all message parts until it
finds text/plain part, and return
it through this property.
In specific occasions, if ContentType is
multipart/mixed, wodMailbox will go
one level deeper and check if any of parts have ContentType
of multipart/alternative - in which
case text/plain content will be
searched among those parts. This is typical message with
two parts (plaintext and html) and attachment.
If plaintext content is encoded, wodMailbox will decode
it before it returns it to you through this property.