UPDATE: Connecting Sumo to any email provider now requires Sumo Pro. If you have already connected Sumo to ConvertKit, your connection will not be broken, but you will not be able to connect any new features to ConvertKit without upgrading. You can still collect and manually import a CSV on their free plan.
Sumo's awesome dev team built the integration to connect with ConvertKit! We've tested it and it works great.
If you aren't already familiar with them, Sumo offers the most powerful marketing tools online—and they are all free to start.
Our favorite Sumo tools are:
List Builder to increase your daily email sign-ups by 20%
Welcome Mat to create your highest converting page
... plus a ton more that are equally awesome.
Activate Sumo + ConvertKit
Once you have Sumo setup you can go into the Services section to connect to ConvertKit. Just select us from the list and enter your API key. From there, select which ConvertKit Form you'd like your Subscribers to go to.