You mean there are no buttons to reply, rorward or move?
Reset the iPhone by holding the sleep/wake button and home button at the same time.
Hold them both until you see the screen go black. In some cases, you may need to keep holding them even after the red power off slider appears. If it does, just keep holding it.
Wait until the white Apple logo appears.
When this happens, you can let go - the iPhone is rebooting.
Kill the mail app grom multitasking gefore doing this.
Ugh! I have 5 email accounts setup across gmail, yahoo mail, icloud and Exchange. That would have been quite painful.
For your future reference, a simple reboot of the device brought the features back. It's disturbing that IOS is going the way of Windows where a periodic reboot is needed to clear the cobwebs, but its now something that I'm aware of for the future.