-The message is
-appended to the file in mbox (uucp) format. This is the format used by most
-other mail clients (such as mailx, elm). If the message can be appended to
-the file, then this action succeeds.
+This is handled by piping the message to the
+.B mmh
+program
+.BR rcvpack .
+If
+.B rcvpack
+returned successful, then this action succeeds.