Every time I have to reboot the Exchange 2010 server, I have one user who loses his mail connection on his iPhone 5. It simply says, "No Mail." I have to then delete the mailbox from his phone and set it up again. It always works again once I've followed this procedure, but it makes no sense why he is the only user out of a dozen who experiences this issue. His mailbox settings appear to be the same as everyone else's, so I'm a bit lost as to what else to pursue.