Each time one opens a message sent from a SPAMmer, there are ways (server logs, etc.?) for the SPAMmer to verify email addresses -- then sell those addresses in a 'valid-email' list; discover whether the message were opened; among other things. I was hoping this video would show me how to access the header information without opening it. One message I received in gmail claimed to be from corporate. Why must I be forced to open the message to be able to ascertain whether the message is SPAM (by looking at the headers) . That an image of a message appeared in the message view frame gave me a second clue that this was SPAM (the first was GMAIL as the from: with no subject: .
Looking through Google Support it appears the only way to obtain the message headers in Gmail is by opening the message and following the steps in this video.
Many spammers use pixel tracking to track messages opening and verify email addresses using this technique. You can disable image loading in all messages using Gmail under the General tab in Settings.