Planetrism and its developers are present on social media. We do not use mailing lists.
Twitter: @PlanetrismGame (for reasons that we do not understand, Twitter administration decided to suspend our Twitter account which contained only pictures and updates about Planetrism. Since this seems to be the style Twitter treats its users, we have no intention to make a new Twitter account.)
Facebook: https://www.facebook.com/PlanetrismGame/
and FB group: https://www.facebook.com/groups/435261330236999/
Channels above are updated infrequently, usually only if there is some major update in game development or something else worthwhile, so there is no fear of constant barrage of spam.
Both developers have their own channels, that get more frequent updates containing work-in-progress pictures, videos and updates.
We also chat on our public Discord channel