-%<{date}In-Reply-To: Your message of "\
-%<(nodate{date})%{date}%|%(pretty{date})%>."%<{message-id}
- %{message-id}%>\n%>\
-%<{message-id}References: %<{references} %{references}%> %{message-id}\n%>\
+%;
+%; Make References: and In-reply-to: fields for threading.
+%; Use (void), (trim) and (putstr) to eat trailing whitespace.
+%;
+%<{message-id}In-reply-to: %{message-id}\n%>\
+%<{message-id}References: \
+%<{references}%(void{references})%(trim)%(putstr) %>\
+%(void{message-id})%(trim)%(putstr)\n%>\
+Comments: In-reply-to \
+%<{from}%(void{from})%?(void{apparently-from})%|%(void{sender})%>\
+%(trim)%(putstr)\n\
+ message dated "%<(nodate{date})%{date}%|%(tws{date})%>."