How do I do simple lead gen and capture email addresses from my website?

I've currently got a simple one-field (email address) form and button to capture email addresses on my website to build a list of people I can email. Right now, when someone submits the form it sends me an email with their address and I add it to a spreadsheet. That information, as a result, is not captured in NS for anyone else to see.

Is there a way to capture emails directly into NS? I just went through the process of creating an html template and did the whole NLFORM form thing, but when I go to create the Online Customer Form it tells me that either first name, last name or company is required, but I only have email address, because that's all I need/want to start with.