Check for valid email after user inactivity?

I do not know about the existence of a plugin. But here is the word of advice.

There can be two ways.

First check the user when he logs in of his activity period. If he has not logged in previously for said period of time, send him an confirmation email.

Secondly you can run a cron job at set time, and check for accounts that has been above some inactivity threshold and send them confirmation email.

I am confirm about this, that wordpress stores login time.