An Application Programming Interface (API) is an interface between one software program and another so they can make use of their services, resources and interact. In e-mail marketing an API can for instance be used to integrate different systems with your email platform, like CRM systems or customer service applications. It can also facilitate the use and synchronization of (external) data. Different email tools can have different APIs, and while some might be very basic, others might allow you to use many 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 webservice. Often SOAP (Simple Object Access Protocol) and XML is used to facilitate the API. That is why some might call it a SOAP or XML integration.