Hi Joan. Welcome to the Forums!
Yes Spoofing, Phishing and all related things are problems all over the internet. There are many ways that they can get addresses unfortunately and new ways being made up even as some of the original methods are dealt with. Some mass e-mail from collected lists from a third party, some collect addresses from websites or e-mails and some actually inflitrate the network systems of organizations and use their own lists against them.
I am not an expert on this and I also don't want depress anyone. On an ending note, the number of legitimate people on the internet far outweighs the number of scammers. Just keep your head on straight and don't believe everything you see. Routers and computer protection software may help also.
Aside from that stuff: Welcome to Auctiva! We hape your experience here is a great one!