It is a requirement of using Cmail that you have our instant unsubscribe link in every campaign. You may want to also capture those unsubscribe requests in your own system, and you can do that using a custom unsubscribe confirmation page.
Every list can have its own unsubscribe redirect page, which is where the unsubscribing reader will be automatically sent to, after they have been removed from your list.
This is how it works:
For example, you could change your unsubscribe URLto:
www.abcdesign.com/unsubscribe.php?user=[email]
The email address of the individual who unsubscribes will then passed into the query string of that page. For example, the subscriber johnsmith@aol.com will now be redirected to:
http://www.abcdesign.com/unsubscribe.php?user=johnsmith@aol.com
Once it's in the querystring you can do whatever you want with the email address server side. This technique will work for anyone who unsubscribes via a campaign or an unsubscribe form.