Substack warns email is becoming less reliable for creators

Creators should not rely on email as a long-term distribution channel, Substack has said, as inbox platforms increasingly filter content and distort engagement signals.

Mills Baker, head of design at Substack, said email is becoming “less deterministically reliable” as a way to reach audiences, pointing to spam filtering, privacy changes and the growing role of AI.

“Apple and Google serve many masters, and do not much care whether the deliverability of this or that type of email declines,” he wrote on X. “If writers and creators get lost in the mix sometimes, it doesn’t concern them.”

The comments followed a note from Substack to users that changes to how Gmail handles tracking pixels have reduced the visibility of email open rates across platforms, without affecting underlying subscriber behaviour. 

According to Substack, click-through rates and paid conversions remain stable, and are a more accurate measure of engagement.

Baker attributed the shift to rising volumes of spam and promotional content leading to more aggressive filtering by email providers, and the increasing use of AI to filter and prioritise emails. Privacy changes, particularly from Apple, have also reduced the accuracy of metrics such as open rates.

He said these factors informed Substack’s investment in its app and feed-based distribution.

"People had many theories for why we launched an app, our own distribution feeds, etc., but the real reason is that we knew we couldn't ensure sustainable connection, and therefore earnings, for creators unless we developed an end-to-end system," he wrote.

Substack has made a series of moves away from its newsletter roots toward a more social media-style model. In January it launched Substack TV, and has increasingly leaned into in-app feeds and Notes as alternative distribution channels. 

It maintains, however, that its model remains aligned with creators. "The only really unique thing about Substack is that we make a fraction of the money writers earn, so we'll never trade-off against their earnings as other companies do," Baker wrote.