I have an email that I haven't shared with anyone that I've been holding on to for years.
What makes you so secretive about the e-mail? Who wrote it?
The email was sent by my father. It said that I was adopted.
Being informed that one is adopted while a kid can be a traumatic event and it is understandable that it has affected you so greatly. You should talk with a therapist about your relationship with your father and seek out greater self-acceptance about being adopted. There is no reason to allow the knowledge of being adopted to upend your life.
My father also told me in the mail that he was a drug addict. Does that make me a bad person too?
No you aren't a bad person. If you are having issues though seek professional help to get through this.