Personally though, I don't get how this kind of marketing strategy works. I unsubscribe SO FAST from things that seem like mass emails that it just wouldn't work on me. I suppose I'm a huge exception to the general public? I'm even surprised when I look over at my girlfriend's gmail how many promotions she has (not in a separate tab).
For example, Indie Hackers (the site that hosts this interview) has grown to about 8000 email subscribers in the past 6 months. My newsletter has 52% open rates and very low unsubscribe rates.
Even more extreme, Ben Thompson at Stratechery has upwards of 2000 people paying him $10/month to get his private newsletter.
It's more of a notification via email than the email itself.
I have a ton of spam promotions that come when I join a service. I want the service, not the marketing!
But sometimes I want to follow what someone says, so I sign up. I read that stuff very attentively.
Services like convertkit tend to be used for the latter use cas: deliberate signups by interested people.
That sample gives you a potential of 50% of the market, and in my experience you are the exception and she is the rule, adjust accordingly.