I think all you have to do is make a file that will store the number of times the mail form has been used. so when someone submits the email, first it looks in the file and sees nothing since it doesnt exist, so it writes the first person on the list, then write a 1 to the file. next time it sees a 1 and sends to the seconds person, and writes a 2 to the file and keep the process until you reach the number of people in the email list, and then reset the count.