I'm afraid the ' sending off' the posting of items is not as important as delivery being proved that is only done with tracking.
Under Simple Delivery tracking isn't needed for items under the value of £10 and letter size, however, if your buyers are opening cases of item not received, this will affect your selling standard.
It's unusual for too many INR cases to be opened, is it the fault of your Post Office is it worth trying another ?
If a case for Item not received is made and there's no tracking you do need to accept the case and refund within 3 days that way no defect is placed on your account.
@nickolob_cards