If you have a newsletter attached to your service, you would increase the likelihood of me signing up if you allowed me to specify a separate email address for it.

I still quite like newsletters. But I don't like them in my default inbox. My inbox is reserved for things I should act on, and the less time I spend moving irrelevant stuff out of there the better.

I use a service called Feedbin for all my newsletters and RSS feeds. I get a unique email address and I go to the website or app to read newsletters when it suits me, not when I'm interrupted. I wrote about this service, and some alternatives, a while back:

https://axbom.com/newsletters-the-mindful-way/

p.s. Yes I know I can create inbox rules, but that puts effort on me. And still expects me to use my default address for everything, which makes tracking easier.