First of all, great plugin! We just moved to it from using sendmail and are happy with the plugin and CMandrill.
A couple of things: we use FSForm for a lot of form submissions. I noticed that the RSForm email process kept reverting to sendmail rather than Mandrill. I think we solved this by making the Cmandrill #1 in the system extensions.
We have another problem though where in RSForm Pro, we specify that an email confirmation goes to the user and a copy is BCC'ed to one of our staff as well. This worked great with sendmail, but now with CMandrill, both the user and the staff email address are showing up on the To: line in the email that the client receives.
Any thoughts on what could be causing this and how to fix it?