If you received an email from them, first do this: If you are using outlook, open the email, then under "View" click "Options" it will show you all of the header material. In the very first line you will see the "Return Path" listed. If it does not say paypal.com in the email address, then it is a fake!
If you are unable to do this, look on the PayPal site for their support email address (you'll never reach them by phone!), and send them the email as an attachment, and explain to them you wish to know if this is legitimate or not.