What is Substack?

What is Substack?

Substack was founded in 2017 by Chris Best, Jairaj Sethi and Hamish McKenzie, and raised a $15.3 million Series A led by Andreessen Horowitz in July 2019. It does not present itself as a newsletter tool: its own about page calls it a media platform where creators earn from subscriptions.

A Substack publication is a website and a mailing list in one object. Every post lives at a URL and can go out as an email to subscribers, and publishing costs nothing whatever the list size. Substack instead takes 10 percent of every paid subscription, with Stripe processing fees on top. Writers set their own prices above a floor of $5 a month or $30 a year, and a custom domain is a one-time $50.

The platform announced 5 million paid subscriptions in March 2025 and raised $100 million that July at a valuation above $1.1 billion. More than half of new subscribers arrive through its own network of cross-publication recommendations and its reader app, which is the asset no standalone email tool can copy. It began piloting sponsorships in December 2025, after years of arguing against advertising, and launched a TV app in January 2026.

One fact outweighs every feature for anyone comparing Substack with an email platform: you never send from your own domain. Posts leave from an address in the form yourpublication@substack.com, and that address cannot be changed, not even by connecting a custom domain, which moves the website and not the sender. There is no SMTP relay and no sending API.