rmail-apply-in-message

rmail-apply-in-message is a compiled Lisp function in `rmail.el'.

(rmail-apply-in-message MSGNUM FUNCTION &rest ARGS)

Call FUNCTION on ARGS while narrowed to message MSGNUM.
Point is at the start of the message.
This returns what the call to FUNCTION returns.
If MSGNUM is nil, use the current message.