Background daemon

if you had initially set it to sending every hour and then changed it
to every day in between, then u may have to re-start the daemon.. did
you do that?
but i second Michael.. you should be using a cron for this.

Yes, I restart, but nothing change. Continuing send the old e-mail.
Send one time the new, but after every hour send the old.

Do you know what I have to do?

Use the delayed_job plugin if you find it hard to tweak scripts to
your taste.