Hello, Most email marketing scripts like Interspire, PHPList, ArpReach etc doesn't support real email throttling (email throttle + domain throttle) even if you customize it. I will suggest PowerMTA installation and setup on your mailserver (Hosting server) which has these features built-in. If your server has multiple IP addresses then it can be rotated too with every email you send. Let me know if you wish to have this setup for you. Kind Regards, Hayder