First write a page to do your daily emails....
Then make it run every day. There are 3 ways I can think of of:
1) Set a javascript timer on the page (for 24hs) and leave it open constantly on your computer. You could never close it though.
2) Set a "scheduled task" to open the page each day from your computer.
3) Use CRON. This runs from the server and the server automatically runs a program at a specified time.... Please dont think I'm an expert on this (I have actually never done it nor do I know how 2).
Anyways - Hope it helps
- Matt