I Wish...
Sometimes I unsub for simple reasons like... you're in my inbox 6 times a day! And other times it's something more personal like, I hate your name.(TREVOR!)
Some autoresponders give the option, and if yours does, I recommend using it.
You can get some ridiculous claims about not ever having signed up for your list, when you know it's a double optin list.. but you can also learn some valuable insight to make your list better and more responsive.
Plus, if your name is Trevor.. I could explain it to you in all caps rage.
Have you tried asking people why they're not signing up, how has it worked for you?
Steve Browne, online business strategies, tips, guidance, and resources
SteveBrowneDirect