A business is a system of systems-but where does email marketing fit in?

Hi all-long time lurker, first-time poster here...

I've been binge-reading this forum a lot the past few days, as I was able to log into my long-dormant account, and have been soaking up the wisdom of certain people on this forum. I then had a question about email marketing:

Jason Kanigan wisely says that there are four systems in every business: Lead Generation, Qualification, Conversion and Fulfillment. Which of these systems does Email Marketing fit into? Is it qualification or conversion? Email marketing could even be split into two skills, no? List-building AND list "nurturing" (for lack of a better term....by nurturing I mean all the story-telling and email sequencing, etc that people put work into in order to keep the list engaged and "warm" so it's ready to be sold to when the list owner wants to send them an offer.)

So would the list building be Qualification and the nurturing part Conversion?

Hope that question makes sense. I tried searching for an answer in the forum search but couldn't find anything.