Introduced property com.openexchange.mail.transport.removeMimeVersionI nSubParts to '' to specify whether to remove superfluous MIME-Version header from multipart sub-parts on message transport.

Specifies whether to strictly obey suggestion in RFC 2045. The MIME-Version header field is required at the top level of a message, but is _not_ required for each body part of a multipart entity. If set to true, each message is processed to not contain a MIME-Version header in sub-parts. Default is false