The MessageFrom property returns the address of the user
who sent the current message. This property uses either the XSENDER
or the XTND XLST command in order to determine who the sender is. The
XSENDER command returns an authenticated address, as used with the
Netscape SMTP authentication method. If this command is not
supported, or the sender's address was not authenticated, then the
XTND XLST command is used to return the value of the "From"
header field in the message. If this command is not supported by the
server, the method will attempt to retrieve the entire message header
and return the value for the specified header field. This enables an
application to use this property even if the server does not support
command extensions.