Once a backup isn't needed anymore, you can always delete the attachment or the entire email to avoid overloading your inbox.
Usually, I create a flash drive backup, but any sort will work for the few days when that particular moment in the ms. is important. By a week later, it typically isn't. I end up with 30 backup files at a minimum while doing NaNoWriMo for 30 days. Have I ever gone back to any of them? Extremely rarely. That's because I've gotten beyond wasting my time writing scenes that won't be in the final version of the story. In the early days, though, every day's work might have included bits that eventually got axed. My first books were true learning experiences.