It happens all the time. E-mails sent specifically to one person, end up getting forwarded to others. Even though it happens all the time, just like many other misconceptions about the online arena and e-mail, that doesn’t mean that it is good practice.
When someone sends you an e-mail, consider it for your eyes only. (And, I have to state this because I will get protests by site visitors if I don’t — this of course does not include threatening or illegal e-mails.) By forwarding private e-mails to others, you are reflecting a lack of character by betraying the trust of the person whose e-mail you are exposing without their permission.
Intentions do not make a difference either. Whether you are forwarding to help or to harm doesn’t make the forwarding in of itself O.K. If you feel forwarding an e-mail to another party can help the person who sent it to you, simply ask their permission to do so letting them know what you hope to accomplish.
E-mails are copyright protected by the author at the time they are created. That’s just how copyright works with written works. So, to forward, publish or post without the original author’s permission is copyright infringement. Take note though; this probably doesn’t apply when on company time using company resources — in the workplace there should be no expectation of privacy.
That said, even in the workplace, one should not forward coworkers e-mails without their knowledge or permission. You may be viewed as petty or untrustworthy depending on your motives for doing so. Either way you have breached a coworkers trust and that can’t be a good thing!
The bottom line? Always ask before forwarding and explain your reasons for doing so.