How did she/he get your address? Did you give that person your email address or your street address? A reply to an ad? A contact on a dating site? Did you divulge any personal information that you would not want made public? You are always free to ignore any emails you didn't solicit (from that person or other unknown parties); there are agencies you can report the person to if they threaten or harass you. Until you hear from this person again, I wouldn't worry too much.