If you don't send regular emails, don't email them all yet. With 95% of the traffic dying down, scale back to minimise costs and work on new project until it's

If you don't send regular emails, don't email them all yet. With 95% of the traffic dying down, scale back to minimise costs and work on new project until it's finished/ready. When you get a new project ready; say something along the lines of "This will be the last email from viral-project. The viral-project closing down, thanks for participating! (Allow option for people to get messages/pm/etc if it's a permanent shut down). I will be focusing my efforts on a new direction: new-project."