Long time Campaign Monitor user, but I have to admit that I have not yet used the Design Tester!
My question: how does it work when I make edits to an e-mail?
For example, if I pay and run the Design/Spam tester on my email, do I have to pay again to retest after making changes to my copy, or when I am troubleshooting a design error in particular e-mail client? Can I continue testing my email until I get all of my problems fixed?
It's $5 per test. If you make edits and test again that would count as another test. It generally doesn't take more than a couple of tests to get things working correctly though.
It would sure be nice if there were a way to redesign and test an e-mail a few times without paying again. Maybe within a given time limit, or by allowing up to 3 or 4 tests of the same campaign or something... at least two tests so that you can verify that you have fixed the problems it said you had originally.