Universal Acceptance is the simple concept that all domain names and all email addresses work across all applications.
A recent Universal Acceptance Steering Group (UASG) http://www.uasg.tech) study found that many users were being denied access to applications because they lacked a simple fix.
Top-level domains (TLDs) and email addresses have evolved markedly since 2010, when non-ASCII characters were first introduced. Hundreds of these new style TLD names, including TLDs longer than three characters, have been added into the root zone. In 2012 non-ASCII characters became available in the mailbox portion of email addresses

http://get.uasg.asia/docs/UA103-Hacks-2019-03-20.pdf