This document defines a "digest" subtype of the multipart Content- Type. This type is syntactically identical to multipart/mixed, but the semantics are different. In particular, in a digest, the default Content-Type value for a body part is changed from "text/plain" to "message/rfc822". This is done to allow a more readable digest format that is largely compatible (except for the quoting convention) with RFC 934.
A digest in this format might, then, look something like this:
From: Moderator-Address To: Recipient-List MIME-Version: 1.0 Subject: Internet Digest, volume 42 Content-Type: multipart/digest; boundary="---- next message ----" ------ next message ---- From: someone-else Subject: my opinion ...body goes here ... ------ next message ---- From: someone-else-again Subject: my different opinion ... another body goes here... ------ next message ------