What makes an email client so difficult to write? I don&#x27;t mean this to sound insulting, I just really don&#x27;t understand where the complexity is. It seems like you should be able to get to a point where it is feature complete and all development efforts shift to maintenance mode. Or maybe I don&#x27;t understand what&#x27;s been going on with Thunderbird and perhaps it&#x27;s been &quot;done&quot; for years now.