Interesting issue with IMAP accounts.

Just an interesting difference I have spotted since updating to iOS seven: I have an IMAP email account. Under the old Ios the iPhone would only download the most recent 50 messages. Under iOS seven, it appears to download everything and there doesn't appear to be a setting to change this. I'm not that bothered, except that this account has over 3000 messages on it and I don't want to use unnecessary space up. I'm not entirely sure why it's necessary to download the whole lot anyway. Any thoughts would be very much appreciated.