It has been a recurrent request from customers to be able to send email
messages to email addresses containing non-ascii characters. [IDNA] is a
domain extension to allow unicode characters in domain names. [SMTPUTF8]
is a SMTP extension to allow unicode in any header.

IDNA defines the [punycode] encoding which translates unicode to an
ascii representation. This encoding MUST be used to encode domains.

SMTPUTF8 is an SMTP extension that allow utf-8 in all headers on the
envelope.

[IDNA] https://tools.ietf.org/html/rfc5890
[SMTPUTF8] https://tools.ietf.org/html/rfc6531
[punycode] https://tools.ietf.org/html/rfc3492



Task: 2116928
opw-2229906
opw-2248251

closes odoo/odoo#47709

Signed-off-by: Raphael Collet (rco) <rco@openerp.com>