Check sender mail address exists with in the Contacts list

Hi all,

I am using Exchange server 2013, my task is to create Service ,that need's to  monitor continuously for new mails and check sender mail address exists with in the Contacts list of my mail box or not.

what is the best way to monitor mail box continuously ? , i need to give this service to PHP team to consume it in their Application.

kindly help with some information or sample code .