I am bombarded by all kinds of unsolicited emails that have "Confidential" written on them, but can I share them with you? What are the legal ramifications of sharing a confidential letter?
Unless you enter into an agreement (sign a document that has confidential written on it), you are NOT legally bound to keep it confidential. In order for it to be confidential, both parties must agree to it.
A prime example is an email containing a winning lottery scam and marked confidential that asks you not to share the contents with anyone. The last thing they want is for you to share it and discover that 1000 other people received the same winning letter. By marking it confidential, they are trying to make you believe that there may be legal ramifications of sharing the confidential letter!
So, unless you have entered into some agreement with the company (or individual), a letter marked confidential is not really confidential unless you sign it.
Note: I'm not an attorney and you should consult an attorney in your area to verify my findings.