You can export customer data by segment within the Segmentation tab within the Admin console. You can download an export of customers' email addresses per segment as a CSV file. This data is useful if you want to send Campaign emails targeted at specific Segments.
To export customers by segment click on the "Export Segment Email Addresses" and you will see the following screen.
If this is the first time you have exported data there will be no files to download. You need to click on "Generate Segment Export Data" to initiate the creation of the files. There maybe a significant amount of customers in each segment so this process is run in the background. As soon as the export files are available you will receive a notification.
You can then download each file as a CSV which will list all the email addresses of all the customers that match within that segment.
As customers can change segments on a regular basis it is recommended that you re-generate the data each time you want to use the data for Campaign emails or any other purpose.
NOTE: If you are creating a new Segment, there will not be any information captured in that Segment yet. For example, if you create a Segment aimed at people who have made one order, that Segment list will be unpopulated until someone makes an order, and then they will be listed under that Segment.