When someone unsubscribes from a Campaign Monitor list, their email gets added to a suppressions list which makes it harder for them to be manually resubscribed to a new list. If an email is manually unsubscribed, it also means they are removed from ALL lists, not just the individual list they were unsubscribed from.
This is generally only an issue that comes up with managing tutor email lists, not ticket purchases.
Log in to Campaign Monitor
Select Lists and Subscribers from the navigation bar at the top
Select Supressions from the menu on the left
Select the emails(s) to reactivate by clicking the checkbox to the left of each entry
Press remove from suppressions list in the bar that pops up at the above the table
Select the checkbox in the modal window that pops up to confirm you want to remove them from the suppressions list
Then Select add back to lists as Active (adding back as unsubscribed won’t work i.e. they stil won’t be receiving emails)
Follow these steps to correctly remove an email from a list without it being added to the supressions list.
Select Lists and subscribers
Navigating to the supressions list
Select Add back to lists as Active when removing the email