MHTML is an abbreviation for "MIME HTML," which is a file format that combines a web page and all of its resources. Most web browsers, by default, save web pages as multiple files, usually a Hypertext Markup Language (HTML) file and an associated folder of resources, which might include images, music or other data. MHTML places all of this information into one file, also called an HTML archive, which is often easier to handle.
One task for which MHTML can be very useful is sending web pages through email, because it can allow an email client to display a web page in its entirety without actually being on the site. The archive format also provides an easy way for a person to view a web page without being online at all. Despite these capabilities, MHTML is subject to some of the same limitations as the more verbose HTML-plus-resource-folder method of saving web pages. HTML archives do not automatically update when a web page is updated online. The files are static entities, providing a snapshot of a page at a particular point in time.
MHTML files can be viewed in a text editor just like plain HTML files. Images and resources that do not have a textual representation are not preserved in the text editor and are shown as strings of random letters and numbers. The source code of the page, as well as the style sheet that governs the page layout, is easily visible. Viewing an HTML archive as text does not affect the display of the web page when the archive is viewed in a browser.
The web page displayed from an MHTML file is not always an exact replica of the page as it originally appeared online. Conversion to the archive format might cause small problems with style sheets, which would in turn cause layout differences between the saved page and the version that appears online. These changes are usually minor, and incorrect margins around images are common. Major layout problems are rare. In general, HTML archives are robust and dependable ways to condense web pages.