I didn't know, this
will be a news !!
I was able to send FUTURE mails from GMail since last year.
Let me tell u the procedure.... (Only thing is that u have to enable POP access to ur GMail account)
Configure your Microsoft Office Outlook with GMail account.
Change ur system date to any future day.
Now, send the mail.
And thats all...
GMail server takes local system date and NOT server date !!