So, I recently sent a message to everyone in my alliance. It was not spam, it was an announcement. Is this punishable? They were about 25 seperate messages.

No, you won't be punished. The maximum amount of messages you can send each day is 200, it doesn't matter who you send them to. As long as you don't use the message system in a destructive manor you will be fine :D.

As long as you did not use a script or a program to do it, and did it via one by one, or CC'ed everyone you are perfectly fine.