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

.ip \fBquit\fP
Leave
.i Mail
and update the file, folder, or system mailbox your were reading.
Messages that you have examined are marked as
.q read
and messages that existed when you started are marked as
.q old.
If you were editing your system mailbox and
if you have set the binary option
.i hold ,
all messages which have not been deleted, saved, or mboxed
will be retained in your system mailbox.
If you were editing your system mailbox and
you did
.i not
have
.i hold
set, all messages which have not been deleted, saved, or preserved
will be moved to the file
.i mbox
in your home directory.