Does dkim-filter need to be running all the time?

Does dkim-filter need to be running all the time? I noticed it's using quite a bit of memory, and I seem to be running out occasionally while i am performing other tasks logged in through ssh.

If it is not required to run all the time, how would I configure it otherwise? Could someone either point me to a link with more info or post any instructions here? I tried searching Google, but I guess I'm not quite sure what to search for.

Thanks, Jeff