You won't be emailed from here. You need to contact Optus directly (Phone, Facebook the Optus App) to discus options (they also don't do email).
If you are prepaid then just recharge your number every 3 months or so. If you are post paid you can arrange for a pause on your account (you won't lose your number as presumably you are paying a monthly bill still?).
Another possible option is port your number to a cheap prepaid provider. Amaysim charges $10 a year for its minimum prepaid service. That will 'park' your number.