Short for MIME HTML, MHTML uses the MIME email protocol to combine items into a single Web page archive file. In the same way that MIME allows for transmission of media-rich emails, MHTML also creates its own "email" in the form of an archived Web page. This means MHTML allows developers to gather an underlying HTML document, along with its embedded images and media, into a single file. This archive can also include linked documents, if the developer wishes, by use of Content-ID URLs embedded with the MHTML document's header.
HMTL and MHTML, while closely linked, have major differences. Any MHTML document utilizes an underlying HTML Web page, but only MHTML can package an entire Web page into a single file when downloaded. In contrast, when saving an HTML document, a computer creates a folder that includes multiple files that were embedded within the original HTML document. These loose files, if accidentally deleted or lost, can make viewing a saved Web page impossible. With MHTML, since all files gather into one archived format, the archival of online Web pages becomes much easier and less cluttered.