I recently wondered how long email deliverability has been a recognized concern. I combined Google and other search results and found what I think is the oldest reference regarding concerns and email deliverability issues. It was published on July 7th, 2003 by Jessica Albon via WebProNews. It was an interview with then President and CEO of Habeas, Inc. The folks at the Radiant Marketing blog have been posting about email marketing and deliverability issues since January, 2004.

Original Email Deliverability Article

Radiant Marketing Search: Email Deliverability