Someone brought up a good question: Do I need to keep my identity a secret in the bomb sent?
Not necessarily. I like the uncertainty of the recipient not knowing ahead of time who is going to hit them, and the uncertainty for the group of not knowing when the next bomb gets posted, but I think it's ok to let them know in the package who gave it to them. If you want to leave them guessing be my guest, but eventually I think they'll be able to figure it out anyway.
And I do feel somewhat like an evil mastermind knowing it all and everyone else being somewhat in the dark, so let's keep that feeling going!