Issue Summary

Inviting users from the user interface with such emails is working:
имейлНаКирилица@primer and 🎵@primer.com
All the above can be invited from the user interface in Jira Cloud and also can be created in Jira DC.
However when you try to create any by using the REST API:
POST /rest/api/3/user
The server will respond with 500

Steps to Reproduce

try to create user with following emails via rest api "/rest/api/3/user"
имейлНаКирилица@primer and 🎵@primer.com

Expected Results

user created

Actual Results

Response{protocol=http/1.1, code=500, message=Internal Server Error, url=https://.....atlassian.net//rest/api//3//user}
Response Body: {"errorMessages":["The request failed. We're not sure what went wrong. Try again and if the problem persists, contact Jira support."],"errors":{}}

What is expected is to have the same behavior for both UI and REST API or the API to not respond with 500 and have a valid message.

Workaround

Currently there is no known workaround for this behavior (other than creating users via UI).
A workaround will be added here when available