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?

dsn handling				rfc6533
logging
++ - international msg
- presentation of local-part in log
-- a log option?
encoding of local_part

++ 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)

flag in spool file

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

enhanced status codes?			rfc5248++

VRFY
EXPN

non-smtp input