If JVM gets crashed then how will I educate my actor to execute rest of 90 messages when I restart my actor.
By persisting the state of the application while it is running, and loading the last state when it is (re)started. In your case, the state of the application is the list of remaining emails. Every time the state changes, i.e. an email has been sent, and the list changes, you have to persist that change to somewhere more permanent than memory.
You can use Akka persistence for this, which I recommend. You can use a jdbc journal with an H2 database if you don’t want an external database server. Alternatively if it’s just a tiny utility, you can write your own file-based mechanism.