I've just added an imap email acct to my iPhone 6 (iOS 9.1). The account is large with a lot of unread emails - this is because I've just switched from using Outlook on a PC to Outlook on a Mac and I need to do a lot of housekeeping. The emails are all visible on the Mac and on the web, and the number of unread emails are correct on the phone but a lot of them don't appear on the phone. I've deleted the account from the phone and reinstalled it but the problem persists, although after reinstalling the account different emails are missing. Might this be to do with the number of emails?