I think it doesn't matter which email ID you use, but since you are curious, I use Windows Live email ID for rewards. Probably it worked for me because I am using the auto-redeem feature and somehow Amazon voucher was not removed from my already activated auto-redeem even though it wasn't available in Redeem section. If I am not wrong, somewhere in January or may be in February, they removed the Amazon and Flipkart vouchers from the Redeem section, but I activated the auto-redeem even before that on 4th January. It still shows for me as you can see in the image I attached here.
In fact, I activated the auto-redeem for the Rs 1500 Amazon Voucher gift card again newly after completing the last redemption for Rs 1500 Amazon gift card. I guess I have to collect points for the next 3-4 months. This is really tedious.
