Great question! Being able to pull in distribution lists from an external app into Constant Contact is something you can do. Unfortunately, being able to send an email from Constant Contact through an external app if not currently a feature we have. I would be happy to pass along your feedback for the want of this ability. If there is an application in particular you would like to use Constant Contact through, feel free to submit this idea as well. At the bottom of every page in Constant Contact is a link where you can submit feedback of your own.