1. The system or service allows you to prepare a series of emails in advance, schedule the times between emails before they are sent, and apply that email "campaign" to an email address list. The emails will then go out at the scheduled times automatically without your continued involvement. This first scenario does not allow for a new contact or prospect to be added in the middle of the campaign and receive the entire group of emails. In other words, if you add a new person to the list after email #2 is sent, they will then receive only emails #3 and later.
2. The sencond type of system or service does all of the above, but also allows the new contact or prospect to enter the system at any time and receive the entire series of emails from the beginning, on the schedule you set up. If you have six emails going out with one week between each, the new prospect can enter the system at any time and will receive all six in order as planned.

