%x Contents of the Xref: header (string)
%D Date of the article (string)
%d Date of the article (string) in DD-MMM format
+%o Date of the article (string) in YYYYMMDD`T'HHMMSS format
%M Message-id of the article (string)
%r References of the article (string)
%c Number of characters in the article (integer)