Really interesting, have you tested the effect on gmail priority inbox? it could explain a higher open rate.. and it would awesome to know that cc is part of their rankings..
[EDIT]- Also, if you all set with labels already, would you mind continuing the test with something like SigBuzz (g apps) to track open rates and keep us posted?
I think he means that it might have an effect on other people's priority inbox. It could be that if an incoming E-Mail has another recipient, GMail thinks this E-Mail might be more important and place it in the priority inbox.
[EDIT]- Also, if you all set with labels already, would you mind continuing the test with something like SigBuzz (g apps) to track open rates and keep us posted?