The basical number which is set in our plugin automatically is 80 emails per a hour.
Plugin settings allow to change it on Settings tab, but its a rate which was recommend by Google developers for not being recognized as spammer.
An important point connected with emails number is also how often are they send. Supsystic recommends you to set it once an hour (as it is set basically). But remind, that if you choose this option and start your newslettering queue it will start in an hour. So do not expect an immediate result, please. If you want just to test our Newsletter plugin, because you are using it first – choose another option, like every minute, every 10 minutes etc.