With Sendit it’s very easy to manage mailing lists and also strongly recommend (by me) you create at least one mailing list for testing use. When activating the plugin for the first time it create a mailing list just to start with the id 1, you can configure and change as you want. From Sendit panel you just have to go to “Mailing list”
You will be redirect in the mailing list page where you can see all your list available and manage!
Go on Edit and set the following informations
Note: if you are using Sendit Pro Template Manager you don’t need to fill <header> and <footer>, if not put some html basic code to give some color and style to your email.