Communities >> Members >> Member List >> Double Opt In Reminder
When the user clicks on the Double Opt In Reminder button, the verification email template opens. However, this template is non-editable, but you can edit the template and make required changes when clicked on "Change Email Preferences"
The Signup Date has 2 dates, Start and End Date. This basically informs the user that in between the provided ranges, if there are any un-verified users, send them the reminder verification email.