I have a hosted Exchange 2007 account and I am running iOS 6.1.3 on an iPhone 4S. When I reply to an e-mail, a grey reply arrow shows up on my iPhone. However, in Outlook, there is no reply arrow. There should be a little purple reply arrow. And a little blue arrow for forwarded emails. Messages that are replied to or forwarded in Outlook or OWA or any other Exchange client exhibits no problems; those little arrows show up everywhere. The exception is when I reply from Mail on an iOS device.