This happens to me all the time, as have my lastname @gmail.com, and my name is not as unique as I thought. I typically contact the real person via some other information leaked in the email.
I once had a lady accuse me of cyber-stalking her, since I texted her when I started getting her Verizon internet information (bills, shipping info for equipment, etc). I finally managed to explain to her that she'd given them the wrong email.