E-mails: When sending out e-mails at that kind of numbers you will need professional IT skills (internal or external) to help you out, otherwise it will be considered spam, and it will not even reach the target. Is there a special pattern for the few responses?
BTW: I am not sure about the laws around the world, but if you did not got permissions, it might actually be spam/not legal?
The survey: I just had a fast look at it, and my first thought is to ask whether you have define internally what (good) service is??? I would start there. Then invite the few responses you got from the survey for some sort of panel discussion, where you can have a dialouge about service. This is much more useful than 8,000 email responses, when it comes to this issue.
After that you might find a gap bettween the companys definition and the customers, and you can make a much more relevant and useful email survey the next time.