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 (+), hyphen (-)
example: uppercase letters, lowercase letters, numbers, dot (.), hyphen (-)
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 you Invite users without registering an E-Mail Address? https://help.teachme.jp/hc/en-us/articles/900005507566