Substack has acquired Yem, a small startup that helps newsletter writers grow their email lists through email marketing campaigns, Substack co-founder Hamish McKenzie told Axios.

Why it matters: The deal is part of a wider effort by Substack to help provide the writers on its platform with tools to grow their audiences organically by tapping into Substack's broader network of writers.

Details: With the deal, all of Yem's employees — of which there are fewer than 10 — will be joining Substack, McKenzie said.

Between the lines: In conjunction with the deal, Substack is also beginning to roll out a slew of new features that will help writers build up their subscriber lists for free.

By the numbers: Early experiments with tapping into its own network of writers to promote subscriptions have so far been successful, McKenzie said.

The big picture: The deal marks Substack's fourth acquisition. The company acquired three small companies last year, including Cocoon, People & Company and Letter.