"Spoofed" e-mails are just like "spoofed" phone solicitations. The sender has manipulated, or "spoofed," the sending address to make it look as if it has originated from a known or legitimate sender.
The experts of the consumer advocacy site Scambook recommend these tips for detecting "spoofed" e-mails:
1. E-MAIL HEADERS. Verify the e-mail is from a known sender first by making sure the e-mail address is the recognized address of the known sender. In Outlook, you can further verify the header by clicking "Other Actions," then click "Message Header." For G-mail, go to the drop-down menu next to the “Reply” icon, then click “Show Original.” For other e-mail services, consult your Tools tab or customer service.