Group Export - Add Email Notification

Goal

To notify the user when their group export is complete, so that they do not have to keep refreshing the export page. This should mirror the functionality of Project export.

Scope

1. The user that triggered the group export is emailed a download link when the export is ready

Copy in the email for Project export:

Project Underscore was exported successfully.

The project export can be downloaded from: Jashkenas / Underscore export

The download link will expire in 24 hours.