网页归档（英语：MIME HTML或MIME Encapsulation of Aggregate HTML Documents，又称单一文件网页或网页封存盘案）为以多用途互联网邮件扩展格式，将一个多附件网页（如包含大量图片、Flash动画、Java小进程的网页）保存为单一文件，可用于发送HTML电子邮件，此单一文件即称为一网页封存盘案，其扩展名为.mht。这种格式有时被简称为MHT。

MHTML是在RFC 2110中定义，然后经RFC 2557修订。MHTML文档的基础是超文本标记语言。

MHTML, short for MIME HTML, is a web page archive format used to combine in a single document the HTML code and its companion resources that are otherwise represented by external links (such as images, Flash animations, Java applets, and audio files). The content of an MHTML file is encoded as if it were an HTML e-mail message, using the MIME type multipart/related.
The first part of the file is an e-mail header. The second part 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 open standard, circulated in a revised edition in 1999 as RFC 2557.