Aaah...In that case everything I said doesn't matter

I have less experience with the BIS settings but have setup a few accounts that way. As long as the IMAPs ports (TCP:993) is open and accessible from outside, I believe BIS will pick that up first.
I am not sure about the secure SMTP connection. I thought that the outbound mail was delivered via your BIS provider, but I could be wrong on that one.