Hi @rntrp,
In AEM, when you send an email using a delivery, the pre-header text that you included in the container is generally not saved as a separate field in the delivery schema.
However, you can retrieve the pre-header text by using the AEM APIs to extract the HTML content of the email message, and then parse the HTML to extract the pre-header text from the appropriate element.
Alternatively, you can use an email service provider (ESP) that allows you to specify a pre-header text separately from the main email content. In this case, you can retrieve the pre-header text from the ESP's API or reporting tools.