The use case here is that a client wanted to send out an email to a selected number of prospects and follow them up two days later. Obviously if you sent the mail out to all the prospects which could be hundreds you wouldn't be able to follow them up in that period and any effect of the email would be lost. So this has to be done in sensible batches and you don't want to send the email out twice to the same person.

So this is how we overcame these issues