Matrix is a UK-based nonprofit whose project is to make instant messaging and VoIP ecosystems interoperable, as the ecosystems on which email relies can be.
The DMA (Digital Market Act) is a proposal for a European regulation "on fair and contestable markets in the digital sector", in other words, a regulation that tackles the thorny issue of control to be applied on large digital platforms(e.g. Whatsapp, Facebook...)
The shared article discusses the technicality of such a deployment.
If it's time to pick up the little ones from school and this gobbledygook bores you, don't leave without this crisp quote:
The bottom line is, we should not be scared of interoperability, just because we've grown used to a broken world where nothing can interconnect. There are tractable ways to solve it in a way that empowers and informs the user - and the DMA has now allowed the industry to demonstrate that it can work. (https://matrix.org/blog/2022/03/29/how-do-you-implement-interoperability-in-a-dma-world#conclusion)
Other articles in Matrix develop this theme: