SpamBot for Google Sheets
More About SpamBot
Once a participant responds, they will no longer get reminders from SpamBot. The admin will receive an update about how the form is going and who has responded so far whenever SpamBot sends out reminders. The app will shut itself off once everyone has responded.
SpamBot must be linked to an active form. The form must either automatically collect the usernames of the participants, or must have a question for users to enter their emails (in which case the admin should rename the column 'Username'). The separate list of emails must have all emails listed in column A starting at row 1.