BillionMail vs Substack
BillionMail and Substack are both email marketing software. BillionMail is open source under AGPL-3.0, with 16k GitHub stars. Substack is a commercial product from Substack Inc.
Which to pick
- Pick BillionMail when
- You want to run your own mail server and campaigns together and know how to manage IP reputation.
- Pick Substack when
- A writer wants to start a free or paid newsletter at no upfront cost and benefit from Substack's discovery network.
Side by side
Bundles a mail server (Postfix, Dovecot, Rspamd) with newsletter and email marketing tools in one self-hosted package.
Newsletter and blog platform with paid subscriptions, podcasts, video and a reader network and app.
Running your own outbound mail server is hard to get delivered; activity slowed after June 2026.
It takes 10 percent of paid subscription revenue, and branding and design control are limited.
Usable
Production-ready
Self-hosted server
Cloud service and mobile app
Go, PostgreSQL, Redis, Postfix, Dovecot and Rspamd
Not published
Open source, AGPL-3.0 (network copyleft)
Closed source, sold by Substack Inc.
Use inside your business is unrestricted. If you change it and let customers use it over the internet, you must publish your changes.
Closed source: you use it under the maker's terms and cannot change or resell the code.
16k GitHub stars
25k Wikipedia readers a month on phones
Young: started 20 months ago, latest release v4.9.
Not known
Other comparisons
More email marketing and newsletter software
Both sides were judged on 2026-11-03 from makers' descriptions, Wikipedia, READMEs and GitHub data. License, age and popularity lines are worked out directly.