For instance, you can send weekly newsletters containing a "tips and tricks" rubric, where you can pot, obviously, hints and strategy guide for better gameplay (example: "if you face a big enemy with many territoryes, cut a way through him and reduce his army spawn number!")
Furthermore you can add some hints of what will come in near future like "shadows" of future races, or clues about features soon to be implemeneted! Or maybe a "coming soon" topic with previews of future game updates.
Also you can add a leaderboard with the best maps, like "editors choice" and "players choice" and "the best 10 maps created".
Besides all of this you can add a link to the forum, if anyone needs to report bugs, players, or just want to talk about the game.
One more idea is a "weekly shards reward" like the daily reward, awarding an ammount of shards (you decide how many).
IIf anyone have more ideas, feel free to post it here!
Waiting for suggestions! 
