Spec documents:
RFC6530 Overview and Framework for Internationalized Email
RFC5890 Internationalized Domain Names for Applications (IDNA):
		Definitions and Document Framework
RFC6533 Internationalized Delivery Status and Disposition Notifications

- rcpt verification for an internationalized message should require the
destination supports the SMTPUTF8 extension

- transport ditto; nonsupport equates to perm-rej an triggers a bounce

- DSN support extended per rfc 6533

======================

++ to-Alabel convert of helo name
++ - smtp transport

++ An "international" flag on the message?
++ An is-international expansion condition?

++ helo-time option handling
++ conversion of utf-8 domains for DNS	rfc5890
-- MSA mode: convert on forward?
--- mua-wrapper
--- acl control?

++ flag in spool file

retries
- apply to a-label or utf8 form?

dsn handling				rfc6533
- ORCPT param: utf8 vs. unitext encoded
-- to/from unitext expansions ( foo\x{HEXPOINT}  - 2-6 hex digits )

logging
++ - international msg
- presentation of local-part in log
-- a log option?

++ Recieved-by header tracking info
++ - WITH protocol types get UTF8 prefix
++ - use for logging also

++ forwarding checks			rfc6530 7.1 -3-
++ - rcpt-time rejects get 533 mailbox name not allowed
++ - mail-time rejects get 550 mailbox unavailable
++ - bounces (see dsn handling)

++ expansions for to- and from-Alabel ?	bug1567

enhanced status codes?			rfc5248++

VRFY
EXPN

++ non-smtp input