What is .mht format ?
MHTML, short for MIME HTML, is a web page archive format used to bind resources which are typically represented by external links (such as images, Flash animations, Java applets, audio files) together with HTML code into a single file. The content of an MHTML file is encoded as if it were an HTML email message, using the MIME type multipart/related. The first of the file is normally encoded HTML; subsequent parts are additional resources identified by their original URLs and encoded in base64. This format is sometimes referred to as MHT, after the suffix .mht given to such files by default when created by Microsoft Word, Internet Explorer or Opera. MHTML is a proposed standard, circulated in a revised edition in 1999 as RFC 2557.
and you can found more information from:http://filext.com/file-extension/MHT:)
The MIME-HTML (.MHT) File Format. Also known as: EML, MHT, MHTML.
Microsoft Internet Explorer uses .MHT files as a “Web Archive” format for saving a webpage will all its ancillary images and stylesheets in a single file.