Introducing Gmail Custom Time. This nifty new future allows you to send emails in the past. You set the custom time in the compose view and the email you send to the past appears in the proper chronological order in your recipient’s inbox. Whats more you can opt for it to show up read or unread by selecting the appropriate option. There are two catches however – You’ll only be able to send email back until April 1, 2004, the day Gmail was launched and secondly each account gets no more than 10 pre-dated emails per year.
“I just got two tickets to Radiohead by being the ‘first’ to respond to a co-worker’s ‘first-come, first-serve’ email. Someone else had already won them, but I told everyone to check their inboxes again. Everyone sort of knows I used Custom Time on this one, but I’m denying it.”

What matter more is the today’s date and Google’s innovation. Though I dont know much about Email servers would not changing the server’s time and sending the mail achieve the same results. Just a thought.