There isn't a way to back date tickets, or import tickets from another source like you are describing using the UI.You could write a custom script that reads your xls and imports the tickets into the database (which means you wouldn't need to worry about back dating since it should take the original data in the date column into consideration) or you could talk to the folks over at: http://osticket.com/customization but that wouldn't be free.)If you do not have the technical know how to write the script or the money to hire someone to do the migration for you, you could disable mail, manually enter each ticket, and then update the tickets date(s) in the database manually, then re-enable mail. It depends on how import historical information is for you and how much you want to spend. A large number of tickets may actually be cheaper to pay someone else.Regardless, what you decide to do you should generally always include the version of osTicket that you are using.