Yes. We tested the script with more than 100 thousand email addresses on several occasions. But remember, it greatly depends on your hosting account. If you have big lists, you should consider yourself a VPS or dedicated server. VPSes comes for $40 / month. And dedicated servers $60.00 / month. So if you really want to use our script to its best performance, you can install it on VPSes/dedicated servers and use it with big lists.