The way we do it is to identify the people we want to drop first, then send them 2 or 3 blasts with increasingly dire subject lines and a huge "opt me back in" button before we unsubscribe them. Somewhere around 1% of people opt back in that way -- even if they haven't loaded images or clicked a single link in years. My impression is that it's mostly people who are reading the message on a crummy old Blackberry or similar device with poor HTML support.
The way we do it is to identify the people we want to drop first, then send them 2 or 3 blasts with increasingly dire subject lines and a huge "opt me back in" button before we unsubscribe them. Somewhere around 1% of people opt back in that way -- even if they haven't loaded images or clicked a single link in years. My impression is that it's mostly people who are reading the message on a crummy old Blackberry or similar device with poor HTML support.