Thing is, any and every e-mail can get spoofed.
One person at an office opens a ‘bad’ e-mail and everyone in their address book gets a virus or a spam e-mail.
So you can get spam from a valid looking e-mail. Or they can get your work e-mail off your work website and spoof it.
Doesn’t matter if it’s yahoo, hotmail, gmail, from your ISP, any and every list can get hacked or stolen. All it can take is one person that you know sending you an E-Greeting card and your address is sold to a spam list (that’s how some of those ‘free’ e-greeting cards make their money, they trade you a free card to sell your data to spammers)
The e-mail address that you never use can be sold by the company you got it from (G-mail, hotmail, yahoo, etc). All it takes is one careless person on your contact list to get your address spammed or spoofed.