HTTP is not a MIME-compliant protocol (see appendix 19.4). However, HTTP/1.1 messages may include a single MIME-Version general-header field to indicate what version of the MIME protocol was used to construct the message. Use of the MIME-Version header field indicates that the message is in full compliance with the MIME protocol. Proxies/gateways are responsible for ensuring full compliance (where possible) when exporting HTTP messages to strict MIME environments.
MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.1. However, HTTP/1.1 message parsing and semantics are defined by this document and not the MIME specification.