Almost as soon as email was invented, it was used as a marketing instrument.
The first unsolicited marketing email was sent back in 1978, and since then spam has continued to grow exponentially. It's estimated that today 90% of all email is spam.
Fortunately the average user doesn't see the vast majority of spam messages. Spam filters are incredibly smart pieces of software, using advanced algorithms to filter out nearly all spam messages. The more you use a spam filter, the smarter it gets as it learns what is spam and what are genuine emails.
Yet sending millions of emails at once is so cheap and easily done that a spammer only needs a few of his messages to get through the filters, and even fewer users to actually buy something from that spam message, to make a profit already.
And that's the core that lies at the heart of unsolicited spam, as well as legit email marketing - it's cheap and it works.
While a spammer is happy with a 0.01% response rate on his spam emails, a well-crafted opt-in email campaign can deliver much higher returns for an organisation.
Smart email marketers have learned to go beyond just sending standard commercial messages. The key is what is called 'permission marketing' - getting the user's permission to send him emails, and delivering what the user expects.
A key approach to permission-based email marketing is newsletters. In a newsletter a company can package its commercial message around interesting and newsworthy content. By combining well-written, engaging content with a subtle commercial message, newsletters can form the solid backbone of a company's email marketing strategy.
This approach has worked well for decades, and is one of the reasons why email marketing is still around after all this time.
Another reason is that email as a communication system has proven remarkably robust. Many new ways of communicating instantly and across vast distances have emerged - instant messaging, text messaging, twitter - but the preferred method of communicating online is still email.
For some reason email resonates with us. It manages to strike a nearly perfect balance between speed and length. Whether it's a one-word message or an email with several megabytes worth of attachments, emails travel around the world nearly instantly and arrive with almost flawless precision.
Because of this our email inbox is the focal point of our online existence. Email and the World Wide Web are essentially different aspects of the Internet, but we've become so accustomed to email that often we fail to realise this. Instead we perceive email as an entirely separate thing.
As long as our daily online journeys start with firing up our email programmes, email marketing will continue to thrive. Unfortunately, so will spam.
Barry Adams is senior digital marketer at Pierce Communications. He once sent out emails to more than a million people. Somehow he still isn't famous yet.