+\fIpackf\fR makes an mbox-style delimiter by examining the first line
+of the message. If the first line is a \*(lqReturn-Path:\*(rq
+field, its address and the current date and time are used. Otherwise,
+if the first line has an \*(lqX-Envelope-From:\*(rq field, its
+contents (which should already be in the correct format) are used.
+Otherwise, a dummy address and the current date and time are used.
+