To do this:
1. Create a CSV file with your first column header of "channels.email.address" and your second column with a header of "channels.email.subscribeStatus".
2. In the first column, place your email addresses.
3. In the second column, place the text "unsubscribed".
4. Import the file into Cordial, selecting "Import all contacts (insert new contacts and update existing contacts)" if you want to both add new contacts and update existing contacts or "Ignore new contacts (only update existing contacts)" if you simply want to update the existing contacts.
Once you upload a list and mark a contact as "unsubscribed", subsequent uploads with values of "subscribed" or "none" will not be honored. This protects from any accidental upload of a new file from overwriting a previously unsubscribed contact. You can manually change the subscribe status of a contact using the UI, or through the "contacts" API.
5. A sample CSV file may look like the following:
channels.email.address,channels.email.subscribeStatus email@example.com,unsubscribed firstname.lastname@example.org,unsubscribed