that your state has and find out what to do. Also, send them snail mail, return receipt requested so they know you can prove they’ve received it. If you have to send it priority to get it there in time, take that into consideration.
I’d also verify the email address and send them the same email every 5 minutes. Some mailers will let you set up a system to do that. That’s one place where being a geek is an advantage becuase it’s not hard to write a program that can do that.