Manual unsub' email sent for deleted user.

Some received one of our manual unsub' emails, but the stated LMA email was '(none)' and the associated user did not exist. - Double-check user exists before sending email?

<img width="662" alt="Screenshot 2024-01-02 at 3 46 07 pm" src="https://github.com/leavemealone-app/roadmap/assets/66140148/b94a8cfa-15e6-4142-aa3a-08fdd1b61897">
