Domain regulations require us to send domain expiration reminders for compliance. It is not optional, and so you cannot turn them off. However, since these reminders are only sent when the expiration is closing in, what you can do is keep your domain name registered for more than one year.
For example, if you keep your domain registered for 2 years, and keep renewing it once a year, you will never receive email reminders because you are always one year ahead of the expiration.
You can do this by manually renewing your domain names for several years at any time or set auto-renewal in your account.