Remove a subscriber from a list in one call:

https://app.feedblitz.com/f?SimpleApiUnregister&key=<api_key>&email=<email>&listid=<listid>

The <listid> parameter is optional. If it is omitted, the subscriber will be removed from all lists within the account; otherwise from the specified list only. Unsubscribing is silent, in that the subscriber is not informed of the status change