Is this true? I have 5 pages of unclaimed jinchuriki packs and 9tails reward, and a compensation from a few months ago. The old mails did not disappear.
Are you not active enough to still have stuff months ago? There's only a page max of 10 after that messages are out from that pages and you can't access them since newer mail are replacing the old ones. This is what is says at the bottom when you open mail:
Log in in order to Post. LOGIN | Register