Whether you've just launched a feature, or it's a year old, you can always learn more about it. You should message your users directly, in-app, to get feedback from them. You need to set up a filter so that all users who use the feature, say, for the 3rd time, are presented with a simple message, asking them to describe their experience. They'll then get that message directly after they use it for the 3rd time.
Once this is set up, you'll be drip-fed a constant stream of qualitative data back into your inbox for as long as you leave that message live. It’s how we inform our feature iterations at Intercom. It works so well because the best time and place to ask for feedback is inside your app, right after your customer uses the feature. It's not OK to send them an email a week after they last used the feature. It’s unlikely that they’ll open it, and even if they do, they’re unlikely to remember exactly how they felt while using the feature.
Some things to remember when taking an approach like this:
Before you can send this type of message, you need to track the specific behavior you want users to take (e.g. File Export) as an event in Intercom.
You should monitor the results as they come in. Turn off the message once you feel that you've received sufficient data. More data equals more time spent analyzing it - so don't elicit more than you can handle, or need.
Pick some customers who give interesting answers (both good and bad), and probe to keep the conversation going, or follow up with a Skype call. These customers are willing to give you honest feedback. How cool is that? Don't pass up that opportunity.
For more inspiration about the types of messages to send, you should check out how we get regular feedback from our customers at Intercom. You’ll pick up lots of tips for targeting your messages to the right customers at the right time.