MIXER is about gatewaying between MIME and X.400 email. Nobody's done anything to it recently, so it's a stable spec, but complex enough to be an useful example. From the announce: MIXER is an update to RFC 1327 which specifies mappings between RFC822/SMTP and X.400 mail. This update corrects several errors in RFC 1327, includes supprot for MIME as well as Internet standards-track delivery status notifications and SMTP extensions to request delivery reports, and defines a standard notation for representation of address mapping and routing information between X.400 and Internet Mail. 2005-10-21