If you read the mail, it states you have to get Six Path Sennin Rank first before your rank matter and it gives you your correct reward.

This means if you are able to get six path in December and in January, you are able to get to Jonin rank - you will get the rewards of a Jonin. You will continue to get rewards based on Ninja School Student until you get Six Path Sennin. This issue has been addressed several times in the past.

Hello, as Danzo stated, the rewards that are stated in the arena interface are the rewards you will receive with that rank after you reach six paths in arena. So, the rewards are lessened before you reach six paths.

OK, Thank you guys