The ContentLength property returns the size of the content
in the current message part as the number of bytes and does not account for
any Unicode conversion of text. Exercise caution when using this property to
determine the size of a buffer that should be allocated for the message text.
If you need to know the actual length of the decoded text in the current
message part, use the TextLength property instead. It will
return the number of characters (not bytes) in the message after it has
been decoded and converted to Unicode.
This property is read-only, and is updated when the current message
part changes.