Those emails come from the Monthly Backup Reminder Service, a monthly email that reminds you to keep backing up the photos and files you would not want to lose. It goes out every month to everyone on the list, so it is not a warning about your drive and it does not mean anything has gone wrong with a backup.
Why you are receiving them
The reminders are not sent automatically, and they are not tied to owning a drive. They go only to people who have asked for them by entering an email address on the Backup Reminder Service sign-up page. If the emails are arriving at your address, that address was entered on that page at some point.
The sign-up form asks for an email address and nothing else.
How to stop the reminders
Every reminder email carries a footer with View in Browser, Manage Preferences, Privacy Policy and Unsubscribe links. To stop the monthly emails, open any one of them, scroll to the bottom and select Unsubscribe.
Receiving them at a different address
To have the reminders sent somewhere else, sign up again on the sign-up page using the address you would prefer to use. If you no longer want them at the old address, unsubscribe from a message that was sent to it.
The reminders are separate from your account and the app
The Monthly Backup Reminder Service is an email list of its own. It is separate from your Ultimate Backup account and separate from the app. Signing up, or unsubscribing, changes nothing about your drive, your account, or the backups you have already made.
If you are still receiving reminders you would rather not get, or you would like a hand signing up, contact us and we will be happy to help.