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

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

helo-time option handling
dsn handling
logging
- international msg
- presentation of local-part in log
encoding of local_part
encoding transform string-expansions
Recieved-by header tracking info