How real is your e-mail?

Asa's presentation in class yesterday was a bit disturbing.  I am still in shock about the capabilities and the harm that this type of activity could do to some one.  Before this we might have been nervous giving out our email because we were afraid of what was coming in.  Now knowing that someone can send stuff from your email without a single password is absurd and mind-blowing.  There really is know way to tell if the email is fake or not, or whether or not people are sending emails under your name.  How disturbing is this?