From the membership database
Select the relevant member status
Fix the members in a selection by clicking "New selection"
Click "Apply temporary filter"
Scroll to the "Participation" and "Events" headings and enter the name of the event
Select the status as "Approved"
Click "Apply filter"
You will now see the number of people who have registered for the event.
Click "Selection" to open the dropdown menu
Click "Remove filtered members from selection"
Click "Selection" again
Click "View members in selection"
You now have an overview of all members who haven't yet registered for the event, in a single selection. From here, you can perform several bulk actions, including sending a mailing.
Selecting members from a filter
If the event is for a specific group of members (Committee, volunteers, first-years only), you can create a simple filter for this via Settings -> Filters -> Create temporary filter. You can read more about this filter in this article.
Navigate to the membership database.
Select the filter you created.
Fix the members in a selection by clicking "New selection."
Click "Apply temporary filter."
Scroll to the "Participation" and "Events" headings and enter the name of the event.
Select the status as "Approved."
Click "Apply filter."
You will now see the number of people who have registered for the event.
Click "Selection" to open the dropdown menu.
Click "Remove filtered members from selection."
Click "Selection" again.
Click "View members in selection."