+## RENAME_HEADERS_ADD(list)
+##
+## Return a newline-separated list of message header additions of the form
+## X-Distorted-Renamed-HEADER: VALUE
+## for each HEADER in the LIST which appears in the current message, where
+## VALUE is the HEADER's current value.
+m4_define(<:RENAME_HEADERS_ADD:>, <:m4_dnl
+CLRSEP<::>FOREACH(<:\
+ ${if def:h_$:><:1:{X-Distorted-Renamed-$:><:1: $h_$:><:1:\n}}:>,
+ <:$1:>):>)
+
+## RENAME_HEADERS_REMOVE(list)
+##
+## Return the LIST, with items separated by colons.
+m4_define(<:RENAME_HEADERS_REMOVE:>, <:m4_dnl
+CLRSEP<::>FOREACH(<:SEP(:)$:><:1:>, <:$1:>):>)
+