Sorry. Fell off the earth Friday and couldn't reply. I'm with you. Convincing clients is a challenge all alone. And I write more the audience who understands what I'm talking about and knows there are grey areas. Opens, clicks, responses, log-ins, forms, purchases, visits with cookies are all bits of data to determine if someone is still breathing. Use anything you have and then weigh if and when you should scrap them.

But don't forget that keeping dead or abandoned addresses eventually puts your email reputation at risk and could be much more costly than keeping subscribers at $3 a head.

You bring a great point so let me ask you. What's your opinion? When should you and when shouldn't you stop sending to unopens. Because you can't tell who has or hasn't opened, what metrics do you use to finally stop sending to someone? You can't just leave them on the list indefinitely for many reasons (cost, spam, etc.) so how do you decide?

How many clicks are your subscribers worth in any given email?