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

.ip \fBset\fP
Set an option or give an option a value.  Used to customize
.i Mail .
Section 5.3 contains a list of the options.  Options can be
.i binary ,
in which case they are
.i on
or
.i off ,
or
.i valued .
To set a binary option
.i option
.i on ,
do
.(l
set option
.)l
To give the valued option
.i option
the value
.i value ,
do
.(l
set option=value
.)l
Several options can be specified in a single
.b set
command.