Email SalesPerson - Overdue Invoices

Hi,

I am trying to work out the best method for the above. The scenairo
is the following;

I would like a process to run everynight which looks at open invoices
This process would look at open Invoices and compare the days date
agains the due date. If the due date is earlier than the days date
then generate an email to the relevant sales person.

I am trying to get into BPM and scheduled processes but not sure how
it all ties together. My initial thoughts are that BPM runs when
something is called such as a transaction? So I am no sure that this
is even the tool.

Could anybody point me in the right direction , I am just looking at
the general direction where I should take this. I would also like the
condition to tigger the email , so that I wouldn't get blank emails
every week etc, which I would get if I used a corvu method.

Thanks in advance.