You'll know if I e-mailed you, the message will be addressed in a logical manner, the message subject will be sensible and related to the message content, the content of the message will be well written and it will be in response to something that we'd previously discussed, and it won't have any malicious files attached to the message. On the rare occasion that I forward a message, there will be an introduction written by me.
To put it simply; I don't spam, I don't even send messages to people who might be interested in what I do. The only internet commerce I participate in is publishing my website here, letting people find it via search engines when they deliberately search for what I do, and responding to any queries that they make.
There's a lot of junk mail being sent around the net with fraudulent details, pretending to be written by someone else, usually written in a nonsensical manner, and often containing offensive or malicious content. At some stage we're all going to receive some of this junk. Some of it is randomly targeted, some of it is addressed to you because they've collected your address from some place that you probably couldn't guess. Likewise, some of it appears to be written by someone that didn't really send it (because the spammer's collected their address from somewhere, and faked that person's details in their spam).
There isn't much that you can do about it, there's nothing that I can do about any junk mail that pretends to come from me (just the same as you couldn't stop someone sending out junk mail with your name and address written on them), nor is their anything that my service providers could do about it.
Don't respond to any spam, don't do anything to encourage more spam (such as buying anything promoted by spam). If they've lied and cheated to get you to read an e-mail, there's nothing about them that you should trust.
Unless you really know what you're doing, and understand the technicalities of how e-mail works behind the scenes, the best way of dealing with junk mail is to simply delete it. You have to be careful when reporting junk mail, as you can end up reporting to the person who sent you it, or getting an innocent third party in trouble. You'll find that most junk mail has faked addressses, and comes from different sources all the time, so blocking one source does little to stop it.
Never “bounce” spam. It's too late, by then, to try and pretend it wasn't received. And you won't be sending your fake bounce back to the spammer, you'll be bouncing it into onto some other helpless victim, spamming them, thanks to the spam message using forged addresses (most do).
One of the better anti-spam systems works by evaluating the content of all incoming mail, and looking for patterns indicative of spam (repeated messages, types of content, etc). You let it analyse the mail you've got, to work out what you want to keep, as well as doing the same for your collection of junk mail (it needs training with both types). Then the next time you receive mail, it should filter any junk mail awail from real mail, you mark any further junk mail that manages to slip through as being junk, and it updates its pattern matching routines. Eventually, it gets better at doing it automatically. If that interests you, search for something that uses “Bayesian” (statistical) filtering, or try out “The Bat!” e-mail program (it's not free software, but it is reasonably priced, and it has Bayesian filtering built into it). That's a Windows program, by the way; there's plenty of other mail programs that have similar features.
Having said that, I'm reluctant to promote the use of anything that automates spam handling. They do make mistakes. It's pointless having one that doesn't detect spam. And it's worse than useless if it flags real mail as being spam, more so if it's deleted without your knowledge. The delete button is one of the most powerful buttons on your computer, enjoy making good use of it.