MIME Encapsulation of Aggregate HTML Documents (MHTML)

MIME Encapsulation of Aggregate HTML Documents (MHTML) is an Internet standard that defines the MIME structure used to send HTML content in message bodies along with those resources referenced from within the HTML. The HyperText Markup Language (HTML) is a markup language used to create documents that are portable between various platforms. One of its key features is the ability to render a document composed of separate resources such as images, sound files, cascading style sheets, and ActiveX objects, in-lined with the marked up text. Many email clients, such as Microsoft Outlook Express are capable of displaying HTML pages just as it would appear in a web browser. As email content, such HTML documents usually include links to other resources that are available on the network.  These resources are identified by the HTML author for inclusion in the page using relative or absolute uniform resource locators (URLs) as attributes within HTML markup elements.  

In many cases, it is desirable to include external resources referenced by the HTML document in the message body itself.  The MHTML specification provides the architecture used to encapsulate referenced resources within the message body, and thereby allows the email client to construct and render the page without retrieving these resources directly over the network.