date email trigger

date email trigger

For my application, my customers contact me by submitting a form on my app, and then I email them back. 

I am trying to make it so, the customer gets 4 days to email me back (so I can tell if they are serious or not), and would like to get an email notification by that 4th day if they haven't contacted me, so I can delete them. 

Any ideas on how to make this happen?

Thanks