An application programming interface (API) is exactly what it sounds like – it’s an interface between one software program and another. This allows the two to make use of each other’s services and resources, and interact with each other.
In email marketing an API can be used to integrate different systems with your email platform, such as CRM systems or customer service applications. An API also can facilitate the use and synchronization of (external) data. Different email tools can have different APIs. They range from very basic to ones that incorporate multiple functions of the email platform. The use of APIs and API integration makes it possible to automate specific tasks. Integration with existing systems or availability of specific API functions can be a requirement in selecting an ESP.
An API might also be referred to as “web API” or web service. Often SOAP (simple object access protocol) and XML are used to facilitate the API. That is why some might call it a SOAP or XML integration.