Creativity not only instills a zest to work effectively but also provides a platform to showcase inherent talents. Remember this while designing any employee engagement activity; you must keep this in mind.
Sending a thought for the day is a nice effort, but are you sure everybody even opens it? Let's say you want to stick to the email activity, and everyone has access to broadband/wifi/internet connection (with speed!). I suggest browsing through a few short videos (animated/short films, etc.) related to HRD or any topic of your choice. Send it across, asking people to vote, rate, or comment on it. Once you get a pulse of the crowd, develop your next activity based on it. You may plan the activities in four phases (one for every quarter, with each successor evolving from the predecessor!).
(P.S.: For starters, send funny/ironic videos.)