Spam is unsolicited bulk email messages usually offering products like Viagra or $100 college degrees. Over 95% of the email Tekserve currently receives is detectable spam or viruses. That being said, how do you avoid all that junk? The first step is to guard your private email address as if it were the crown jewels. Only give your email address out to people that you personally know. Get a secondary “junk” email address with a free service such as Google Gmail, that you can use for registering for websites, contests, or downloading software. Try not to post your real email address on any websites—spammers troll websites and add any email address they find to their lists. You can figure out if you you've posted your email address online by doing a Google search for your email address in quotes. Search for "firstname.lastname@example.org" (with the quotes) and then do your best to get your email address taken off any pages that are returned in the results.
Apple’s Mail application has a junk mail filter that you can train to become quite effective. Go to Mail > Preferences > Junk Mail to check your settings. Mail learns which email is spam as you teach it. Anytime you receive spam, select the message and click the junk mail button (next to delete). Check your brown messages regularly and if Mail has mistakenly marked a message that is not spam, click the not junk button. The more you train Mail, the better it becomes at catching spam on its own.