How to stop invitation reminders

I'm looking to see if anyone has worked with Smartsheet to stop invitation reminders. A colleague recently shared a Dashboard with a Smartsheet group of 300+ users including some external users (customers). He forgot to uncheck the email notification.

Users are now on a second round of reminders sent from Smartsheet, reminding them to access the dashboard.

A couple questions.

  1. Is this an invitation that is triggered for users who are not yet created in our company's Smartsheet tenant? Notice the text on and adjacent to the blue button. Open in Smartsheet to create your account and get started. Or is the reminder sent to everyone in the group, until they open the dashboard?
  2. Has anyone worked with Smartsheet to clear these reminders? I'm betting it's something that can only be done on the backend of the software.

Thanks for any feedback

Answers