php scripting help

HI

I am designing a free website app for realtors to help with there listings using php and mysql. The code That i am having trouble developing is agents need to be able to send emails to there customers that are timed and sent automatically. For example the clients email is sample@example.com i want to send a message to that email every 2 weeks and the message is "this is a test email" that is the code i need. Keep in mind that the site i am devoloping is a free service no strings attached. If payment is necessary we may be able to work something out. Please let me know by replying to this message or by sending me an email geoffism@mail.com


Thanks
Geoffism