Email Planner is used to schedule your emails template.  

For example, if you want to send weekly newsletter for the latest products in your store follow the below steps

1. Create an email template for latest products newsletter and use the custom usercode for displaying the latest products. 
2. Using email planner, set frequency for this template to be sent to a particular email group every week on a particular day.
3. You are done.

Now the extension will send the email newsletter every week to that email group triggered by the cron job until you disable / delete the email schedule. This therefore will be an one time setup for forever customer newsletters.

For this extension to work you need to set a cron job to run once everyday. The cron job script will check all the scheduled emails for the current day and composes and sends the email to the cron bucket list.

Please note this extension will not send emails. It will only compose and saves as draft to the cron bucket list (under Email Template Designer Section). To send the drafted emails from the cron bucket list, you need to setup another cron job that will run at any given time and at number of frequency everyday. The task of this cron job script is to empty the cron bucket (sending emails) in batches. This script will ensure your email server is not overloaded.

Video Demonstration