Email addresses that meet the following conditions can be registered.
xxx@example.com
Characters available for each part
xxx: uppercase/lowercase letters, numbers, dot (.), underscore (_), percent (%), plus (+), minus (-)
example: uppercase/lowercase letters, numbers, dot (.), minus (-)
com: uppercase/lowercase letters, and "between 2 and 10 characters"
* For any part, avoid consecutive dots such as "..".
Uppercase and lowercase letters are not distinguished.
Related: Can I invite users without registering an email address?
https://help.teachme.jp/hc/en-us/articles/900005507566