If integration with your preferred Email Service Provider is not available in the corresponding menu, you can always integrate it via Custom HTML Form.
Here are the steps:
First you need the form code. In your Email Service Provider, go to the desired list/audience and then create a form to collect emails for that list/audience. Then retrieve the HTML for that form.
In Spotlightr, go to App Settings >> Integrations >> Add Integration, select Custom HTML Form:
Name it descriptively and paste the code into the appropriate field. Click on the Create button.