+.BR Envelope\-From :
+.RS 5
+Used by
+.B post
+to specify a value for the sender's envelope address to the mail transport
+system. If omitted,
+.B post
+will use the value of the \*(lqSender:\*(rq or the \*(lqFrom:\*(rq header.
+See
+.IR send (1)
+for more details.
+.RE
+.PP