[Plugin: Subscribe2] Not working

Hi! Subscribe2 was working fine on my wordpress blog. But after it was migrated Windows server to Linux early this month, it is not able to notify my subscribers (about 2,500) because my SMTP server allows only 300 messages per hour. Could someone please tell me how to ensure that only 300 messages are sent per hour? This way, in about 9 hours I should be able to send messages to all my subscribers. Please help.

Vishwas
http://www.writechoice.co.in

http://wordpress.org/extend/plugins/subscribe2/