This email is sent to unverified users when they don’t verify their account before Grace Period. If you do not want to send out this email, you can set the grace periods to 0 from Settings > Security screen User Verification section.
Thank you so much for your speedy reply! I did as you suggested.
Wouldn’t it make more sense to the users to say “Since you have not verified your account, we will delete it. However, since we would love to do business with you, please feel free to re-register and let us know if you have not received your verification email”?