Control rich previews for attachments

Enabling this policy defines a semicolon-delimited list of file extensions which will be allowed to have rich attachment previews. When this policy is disabled or not configured the default settings will be set to . bmp;. emf;. gif;. jpg;. jpeg;. png;. wmf;. wrn;. txt;. err;. xml;. cpp;. c;. h;. cxx;. hxx;. idl;. cs;. vb;. idl;. xsd;. doc;. docx;. xls;. xlsx;. ppt;. pptx;. vsd;. xlsb;. xltx;. dot;. rtf