Email is one of the oldest protocols (ways of transferring data) on the Internet. In fact, it evolved from a simple messaging system on the precursor of the Internet called Arpanet in the 1960s. Like that bacteria that hasn't evolved for 2 billion years, Email as remained largely unchanged in all that time except perhaps for our dependence on it.
The pernicious spread of Spam (officially know as Unsolicited Bulk Emai or UBE) has made electronic mail seem like a necessary evil. Major Email providers like Google have developed some pretty sophisticated systems of filters to protect your inbox. As a provider of Email servers ourselves, we have worked really hard to protect our users from receiving spam and our servers from being vulnerable to sending spam. Our efforts have mulitple layers and each one is fraught with trade offs. Here's a brief, not too technical description of some steps we've taken particularly in keeping spam out of our user's inbox: