? 2 Change Mass Mailer Settings

I want to increase the amount of emails the mass mailer sends out. Ive read in the forums that it is 20.

Does anyone know where this can be changed..

What I decided to do is ad extra cron job and have both them run twice a hour. So I now have my mass mail being sent every 15 minutes which is probably best to keep them as small as possible. But I would still love to know how to change this setting