In order to check inside Microsoft Outlook Rich Text format attachments, a separate decoder program is required to unpack them. Fortunately, this is very simple to build and install.
However, if you have problems building this program or you find that it cannot decode some of your Outlook Rich Text messages, a Perl alternative is provided which you may choose to use instead. To use the Perl decoder, set the configuration option "TNEF Expander = internal" in your mailscanner.conf configuration file.
If you wish to use this TNEF decoder and have trouble building it, or it won't compile, then I suggest you read my notes on compiling with Solaris and gcc.