Oh, spam. There is so much of it. Some estimates say that 90 percent of email sent around the world is spam. Sometimes it's hard to sort the wheat from the chaff; or the ham from the spam.
It's been a plague since the earliest days of the Internet. Whether it's spam that contains attachments—which, if opened, could hijack your computer (though most often, these attachments carry Windows malware)—or phishing emails that try to trick you into entering your bank or Apple ID credentials on dodgy websites, spam is both an annoyance and a danger.
There are several ways you can block spam. If you use Gmail or iCloud for your email, there are built-in spam filters. In Gmail you can view your spam to check for any legitimate email that has been filtered as noxious, but you can't do this with iCloud. Much of the spam that iCloud gets is simply deleted, and you don't even know about it.