Create, Perform, and Delete Email Send Definitions
You can use email send definitions to send emails using SOAP API. Email send definitions are known as email message interactions. This helps you maintain a integration between your external system or development environment and Marketing Cloud Engagement.
Use the sample code below as a model for creating your own API calls related to email send definitions.
When you update a user-initiated send definition via the SOAP API with the Email object, you must set the EmailSubject property on the email send definition. If you don't pass the new subject to the email send definition, it retains the old subject for that definition.