I have gotten up to 40 people on my mailing list, which is a round number and Not A Bad Start. ☺️
Maybe it's weird or brand-ish to celebrate essentially marketing numbers like this? IDK. Losing my author platform really made me worried I wouldn't be able to convince a publisher I could move copies. It matters a lot to how they acquire a book— what your advance is, how they place it on their list (and thus your access to their sales and marketing channels which you can't get by other means). That kind of thing.
What comforts me just a tad is that book marketing (outside of non-fiction self-published kindle sales) is reasonably difficult to find concrete info about. On the off chance anyone is interested...
Here's a case study involving Little Fires Everywhere and how it was marketed:
Your First Thousand Copies (Tim Grahl; more focused on non-fiction but still useful):
General Communism, writing, and shitposts.