V8/usr/src/cmd/Mail/manual/cmds/z

.ip \fBz\fP
.i Mail
presents message headers in windowfuls as described under
the
.b headers
command.
You can move
.i Mail's
attention forward to the next window by giving the
.(l
z+
.)l
command.  Analogously, you can move to the previous window with:
.(l
z\-
.)l