From Outwar Wiki
Outwar has a in-game message center, where you can send messages to other players and to your entire crew. (If you are in a crew and have the privilege to do so from your crew leader)
You will also receive the latest announcements from Outwar in your message center.
You may also choose to receive messages when you get a new Trade Block offer, have a tradeblock offer accepted, get an ally request, or receive a crew invitation. These settings are adjustable at the bottom of the preferences page.