You can register an E-Mail Address that meets the following conditions.
xxx@example.com
■ Characters available for each part
xxx: uppercase letters, lowercase letters, numbers, dot (.), underscore (_), percent (%), plus (+), minus (-)
example: uppercase letters, lowercase letters, numbers, dot (.), minus (-)
com: uppercase and lowercase letters, and must be "2 to 10 characters"
※ For any part, please avoid consecutive dots such as "..".
Uppercase and lowercase letters are not distinguished.
Related: Can I Invite users without registering an E-Mail Address? https://help.series.teachme.jp/hc/en-us/articles/63062075175449