This project puts a sensor into the mailbox down by the street. When the mailbox door is opened, it can send a signal to the home monitor (PC). If it can detect the presence of mail in the mailbox, then it could indicate when the mail has been removed, as well as indicate when new mail arrives.
Just for fun, it could send an email to let you know that paper mail has arrived!
This is purely in the thought stages at this time, so I don't know what might appear here...
Candidate solutions are presented in the order of most appealing, based on simplicity to implement and of course the cost of the implementation.
A simple wireless transmitter, probably coded for noise rejection. The receiver can be in the house, and it could then relay the indication from the transmitter to the PC, and then to the network.
SitePlayer has a couple of basic logic inputs that can be polled. This solution cannot send an email, unless the home PC is the device that initiates the mail after polling the SitePlayer.
Using a Rabbit, which is natively programmable, and has enough I/O, it should be simple enough. It could be polled as a web site (same as the SitePlayer), but the Rabbit reportedly can also send very very small emails using UDP transactions.
EtherNut could easily do this. Plenty of I/O. Can originate communications to the home PC and can send email, host a web server, and more.
TINI could easily do this. Plenty of I/O. Can originate communications to the home PC and can send email.