If you receive a separate email or telephone request request from someone on your contact base to remove them from your marketing list, then it's possible to do that manually in Mitingu.
1. Go to Contacts and select/search for the person who has requested to be unsubscribed
2. Click on Edit
3. Check the box that says The user does not want to receive marketing emails
4. Their contact record will be updated to show they have opted out from all marketing emails