BACK DATE EMAILS SENT

I HAVE 5 DIFFERENT EMAILS THAT I WANT TO HAVE BACK DATE. I WANT IT TO APPEAR IN THE SENT FOLDER OF MY DOMAIN NAME CPANEL AS THOUGH IT WAS SENT ON A SPECIFIC DATE I SPECIFY, WHICH SHOULD BE A BACK DATE. EXAMPLE, I HAVE 5 DIFFERENT MESSAGES THAT WERE NEVER SENT OUT, BUT I WANT THEM TO APPEAR INSIDE MY EMAIL SENT FOLDER AS THOUGH THEY WERE SENT OUT ON A SPECIFIC DATE IN THE MONTH OF AUGUST TO SEPTEMBER. CAN YOU DO IT? LET ME KNOW WHAT YOU CAN DO, HOW LONG IT WILL TAKE YOU TO DO, AND HOW MUCH.