IDN characters are non-Latin and/or accented characters.
All Web servers or Mail do not accept UNICODE (IDN characters) and many will therefore not be able to recognize an internationalized domain name with characters not defined by the standard ASCII (non-Latin and/or accented characters).
It is therefore strongly recommended to use your IDN domain name in PUNYCODE format for your email address.
What is Punycode / Unicode ?
Punycode is a special encoding used to convert non-Latin and/or accented Unicode characters to ASCII (unaccented Latin characters), which is a smaller, restricted character set. Punycode is used to encode Internationalized Domain Names (IDNs) in such a way that the domain name can be read by all systems. A domain name encoded in Punycode always begins with "xn–" to signal that the encoding is being used.
Some useful tools and information links:
• SafeBrands IDN/Punycode Converter: https://home.safebrands.com/services/idn_punycode_translation
• Punycode converter: https://www.punycoder.com/
• Afnic IDN Converter: https://www.afnic.fr/en/domain-names-and-support/everything-there-is-to-know-about-domain-names/create-a-domain-name/
• ICANN Internationalized Domain Names: https://www.icann.org/resources/pages/idn-2012-02-25-en
• International email: https://en.wikipedia.org/wiki/International_email