What can be used as the account name for a user in Active Directory on Windows 2019 Server?

In Active Directory on Windows 2019 Server, the account name for a user can include certain special characters, and the dot (.) is one of those accepted characters. The preferred format for user account names often uses a period as a separator, making "Philip.Thomson" a valid and commonly used format for distinguishing first and last names.

This format helps maintain readability and is in line with common naming conventions in many organizational environments. In contrast, the other choices contain characters such as brackets, commas, and colons, which are not permissible for Active Directory usernames. The presence of these characters would result in an invalid username, whereas the use of a period aligns with the rules for creating standard user accounts within Active Directory setups.