Read by recipient option isn’t accurate – Email Client - Boomerang Mail Review

I did a little experiment on the app. I did send an email to my different account to see if it will indicate “read by recipient” surely enough, it did when I haven’t even open the email I did sent to my my different account. It makes me wondering whether it is accurate or not.
Review by Diligence61 on Email Client - Boomerang Mail.