Given that simming is starting today I think, will you send out one of those global e-mail things to tell people that they've got something to post for now? Also, maybe send one to players without contracts but who are registered to the sim to maybe entice them back?
Keep the mailbox spam to the minimum imo. That or go the other way and send weekly newsletters and shit. If people didn't take notice of the first one they probably won't for this one either.