Apparently, the iPhone 5 is having issues with push notifications from Microsoft Exchange accounts. This means that if you are using your iPhone 5 to check your Exchange email, there may be a significant delay between when an email makes it to your account and when you see it on your phone. Some users are reporting that they are having a similar issue with Gmail and Yahoo email accounts, but Exchange accounts seem to be giving folks the most trouble.
We also saw this issue on an earlier iPhone model that was recently updated to iOS 6, although it seems that some users with earlier models are getting emails just fine. Regardless, just be aware that email pushing could be an issue.
Of course, it's not uncommon (although it is unfortunate) for companies to release new technology to the market without having worked out all of the bugs. This kind of thing is fairly easy to fix with a software update, though, and it appears that Apple is working on an update to fix this issue already. For now, there are some temporary fix methods that we'd be more than willing to help you try. Just give us a shout.