I would like to use Round Cube in way that will not cause problems with my hosting company that restricts the number of email sent to 500 per hour.
For example, I would like to load 2000 emails in the TO: field and have the system send the emails one at a time say every 15 secounds.
So , is there a addon, pluggin or script that will acomplish this task. ?
I'd highly recommend that you consider using a service that is setup to deliver high volumes of mail like MailChimp. While there are ways to use RoundCube that would allow you to do staggered sending other restrictions by your host would probably make it very difficult to have it work correctly.