I will never put my newsletter behind a paywall, because building an audience of readers is more important than a few monthly subscription dollars. I don't want the friction of payment to stop people from subscribing & reading.

Of course, if you have high quality and valuable content that you can provide to readers who have the desire and budget to pay for the content, then you can try a paywall.

I'd rather build a larger audience and then monetize with products and/or services, or ads/sponsors.