USA proxy question about legality

Does anyone know if it's legal to send email through an open proxy in the United States providing there is no commercial element to the message?

For example... can I send as many emails to people as I'd like through proxys if I'm just saying hi?

If they are your contacts I don't believe there is a problem. If they are not subscribed to your e-mail list then it is illegal.

I thought that was only if you were sending commercial emails--something that promotes a product or website. I'm trying to find the specific legalities for sending personal emails.