We had to sunset email lists due to a spam deluge in 2021: Lists.ocaml.org: service temporarily sunsetted
(and noone has stepped up to offer to maintain such a service, and I’m not surprised)
As for alternatives, the most obvious solution is using this forum to discuss issues around the platform. I didn’t see the GitHub issue ping on that PR you created since I have >10000 unread GitHub messages in my email, and I can no longer keep up with that traffic.