Write the email and move the mouse cursor over the 'send' button
Then fasten a pulley to the roof above the mouse and thread a rope through it. Hang something heavy and pointed right above the left click button on your mouse and then at the other end hang a bucket full of water.
Check that the heavy object is capable of lifting the bucket when empty and either punch a very small hole in the bucket or wait for natural evaporation.
When enough water is gone the bucket will raise and the heavy object will press the mouse button and send the email.
Simples.