Mailing list archives are usually delivered over the Web in HTML or Unix mailbox form. HTML is a wonderful way to deliver the data to standard web browsers, but is not appropriate for handling in standard mail reading software. The Unix Mailbox format is very compatible with mail readers, but it has no way to manage the enumeration of mailboxes, or to report metadata about mailboxes which would allow the user agent to select the appropriate one. XMADL fills in the missing piece. It allows the mail archive server to deliver a compact index of MIME-encoded mail messages or MBOX-encoded mail boxes so that the user agent can present the archives to users without downloading all of the messages.
An XMADL document consists of a series of msg and mbox elements. Each msg element describes a mail message. It must have an attribute "href" that points to It contains sub-elements in the namespace "mime" (more info) and "xmadl:representation" elements