lockfile -ml and -mu

Is this a correct way to use lockfile as follows?

%cp /var/mail/furu furu.mbox
% --- edit furu.mbox here! ---
%lockfile -ml
%cp furu.mbox /var/mail/furu
%lockfile -mu

I occasionally need to edit mail spool
because I get "no From line" when I try to read mails using Mail/mail
while testing new procmail recipes.

_/_/_/      Mitsuru FURUKAWA      _/_/_/
_/_/_/        Tokyo, Japan        _/_/_/
_/_/_/     mailto:furu(_at_)009(_dot_)com    _/_/_/
_/_/_/  http://www.009.com/furu/  _/_/_/