Ladywolf, that's simply not true.
I know what Beth is referring to, but at the present time as the law currently stands if mail is addressed to the employer's address, they do have the right to open it. I'm not saying that may not change and I'm not saying they should do it, but the law has not been violated.
The poster should not be having personal mail delivered to the office in any case. That's simply inappropriate no matter how you slice it.