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Same issue on my boss's phone 4. "no sender" "no subject" but when he tries to open it up it won't. When he closes mail then re-opens mail the "no sender" messages disappear. He's also getting messages from ATT now that state that he's way over his data limit and they will begin charging him for going over. The thing is, he's not a power user, not surfing the net, not downloading any movies, nothing. I think his data usage has to do with this mail problem... My iphone 4 doesn't do this but his wife's does. Again, she isn't a power user either so ?