Your renters should fill out a temporary forwarding notice with their back-home post office to have their mail sent from their home to your villa. It probably wouldn't hurt for you to let your post office know that you'll be receiving their mail at your villa for the specified timeframe. This will only forward first class mail, I believe.
Another option: Your renters could ask one of their neighbors back home to bundle up all their mail every so often, stuff it in an Express Mail envelope/box (that they would have bought for them, of course!
), and send it to your villa address. This method would ensure that they'd get to see ALL their mail.
Bill