Customer Satisfaction Surveys - How to increase customer responses

I'll make this discussion very simple. Our customer base is mostly SMB with the rest a mix of midmarket and large enterprises. I took over CS a few months back and right away I looked to get some customer feedback on their feeling about a number of things. The response rate was dismal to say the least. I used Survey Monkey but send the surveys using our corporate emails. I also tried a very small scale survey regarding value for a small targeted group of customer POC using Survey Monkey and sending it from there. Responses were very low.

What's the best approach when dealing with SMB and mid market accounts to get a larger response rate?