I like @btcmelody 's suggestion for substack. I have a running blog (that I'll share here when I have a bit more content and get into a rhythm of posting regularly), and have thought about moving it there. Substack allows anyone to read but you can create subscriber-only content (pretty sure), and similar to nostr it encourages quality content bc the revenue is all subs based, not ads based.

Have you checked out all the standard email marketing providers and found them not to your liking? Not sure what all their requirements are, but constant contact, myemma, and mailchimp are a few of the biggies. There are so many.