If you right click an select View Message Source, you can see the actual address it came from. I had one the other day that was from PayPall - with 2 "L's". That's how I knew it was a fake.
Anytime you get something from PayPal, eBay, a bank or credit card company, etc., you should take the time to check if is legit before you open it.
It's always best to type a website in directly, rather than click on the links in the emails. :)