Earlier this week I got my 700th subscriber to my newsletter. This is up from 250 in June, when I first decided to try to grow my audience.
I've only emailed my audience 6 times since June. Open rates have been 50-60% and CTRs at 15-20%. I don't publish many articles but the ones I do are very deeply researched.
Most of the traffic has come from organic search + word of mouth, plus some spikes due to being featured in industry newswraps and some social media posts that do well. I don't get very much web traffic but the traffic converts well (5-10% of visitors sign up for the newsletter).
Most of the signups come from relevant, high-value content upgrades. My blog is about biotech finance, so I often provide an excel spreadsheet that walks through an example in exchange for emails. I've also added more prominent "subscribe to the newsletter" links at the bottom of articles that convert well.