According to you, is 6% opening rate on mass mailing campaign a good score ? That's what I have now.

I believe that the X in X% opening rate does not mean much. You need to go deeper. Why? Think about this: - If you send a mass e-mail to your 100 closest friends, the OR will most likely be much higher. - If you are sending a mass e-mail to 100,000 emails, it will probably be lower.