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. wodPop3 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, wodPop3 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, wodPop3 will decode it
before it returns it to you through this property.
This property is available only if full message body was
retrieved, not if only headers were retrieved.