I think that the local-part is the smallest of the problems. local-parts are
uninterpreted and can thus carry any encoding that would be a valid
local-part in rfc2822, e.g. rfc2047.
even if the recipient MTA could handle rfc2047 encodings:
- this would still break other message handling software that depends on
being able to compare addresses for equality (since 2047 encoding
doesn't have a canonical form)
- existing MTAs and gateways that translate 2047-encoded character
strings would cause addresses to be rewritten to a form in which
they would not be valid.
2047 would be a poor choice for the encoding of local-parts.
far better would be to use an encoding similar to that used by IDNA,
since local-parts and DNS names have similar requirements for matching.
Keith