Sending a message from the future to the past.
Do We Have This One, Needs More Examples, Needs A Better Description, Up For Grabs. A Time Travel Trope. So you haven't quite worked out how to send yourself or other people back in time yet but you can send a message back. A D-mail is where you send an E-mail, Text, Video or any other data back through time. If it works properly then you can change history from the comfort of your own time. Though you'd need to have ripple proof memory to be able to notice it. Could in thoery be used to send messages to the future too. D-mail is short for De Lorean mail which is named after the time machine in Back To The Future, although the idea for the name comes from Steins;Gate. Contrast with Write Back To The Future, which is pretty much the inverse of this but useing The Slow Path rather than some sort of time machine.
Examples:Anime and Manga