Experian CheetahMail believes that opt-out email appending is no longer an acceptable practice, and that marketers should no longer use of this practice to acquire customer email addresses. EmailResponsibly
In my experience, appending causes major delivery problems. Of course, every time the issue comes up some marketer tells us who think it’s a bad idea that they successfully used appending and it worked and all the delivery problems are a figment.
Maybe the supporters will believe Ben and Experian / CheetahMail that appending is not a good thing to do. After all, Ben was a large proponent of the practice many years ago and Experian still sells appending services in some countries.
Sending mail without permission, which is what appending usually is, will cause delivery problems. Stick to real permission, not vague promises.