Spam can come from several things that we do while using the Internet.
  First and most frequent is when we signup for free items on a web site.

Most likely these sites ask for personal information and especially email addresses. An innocent act, but now you are on a mailing list.

Remember to limit giving out your e-mail address on the Internet.

The next most prominent way to get on spamming list is from answering those emails that come to you that you know are Spam.

 You may even be asking them to remove your email address 
from their list.

    Doing this now confirms that your email address is a "good"
 address and although they may remove you from their list, your
 address can now be sold with thousands of others to other companies that you will now receive Spam from.