I'm starting completely from scratch, with no mailing list.
I don't know anyone else in the entrepreneurial space - my network is all in the arts!
So have started writing a newsletter prior to launch. My aim is 8 editions (it'll be monthly) before I launch to give me some runway. I'll be using Aweber for the mailing list.
The newsletter is called "The Brohug" and is a practical and fun look at male friendship and support - including simple things subscribers can do to support their male entrepreneur friends.
It's great having such a specific niche as it really helps to focus the content.