Integration basically allows data from one device or system to be read or manipulated by another. Essentially, your developers can write a software program that runs on your servers and invokes actions in your email system.
For example, actions like uploading lists and triggering emails can automatically happen behind the scenes. Imagine sitting at your desk, working in your CRM system, and identifying a list of 5,000 contacts to send a reminder about a webinar. All you do to start the process is click a button. Then behind the scenes, using the Application Programming Interfaces (API), your CRM system sends the list of contacts to your email system. Then you click another button and a reminder email is sent from your email system to that list of contacts. Voila!