I have a contact lsit and I want to send them mails.

Case:Each 15 day send them a mail but not send to mail who was in the list which are in the first 15 day list.

Example :Today I have 45 contact and  I send 45 contact email after 16th day I have 54 contact but still do not send mail.Day 30 I have total 200 contact send mail but do not send first 45 contact whic is in first 15 day list.How can I write with deluge.