What is “Content-Type”?

The Content-Type header defines what kind of data a part of an email contains—plain text, HTML, image, audio, or even a calendar file. It also indicates how the message is structured, such as `multipart/alternative` or `multipart/mixed`.

Common Content-Type values include:

`text/plain` for plain text `text/html` for HTML code `application/pdf` for PDF files `image/jpeg` for images `multipart/alternative` for text and HTML versions `multipart/mixed` for attachments

Think of it as the manifest on the cargo deck. It tells the recipient what is on board and how it’s packed.