In the Find External User dialog box, you search for a user in an external authentication provider.
With any authentication provider, you can use the “By user name” option. The name that you enter must begin with a letter and may contain one wildcard character.
With LDAP and MSAD, you can use the By Name or the By E-mail option. Both options require an exact match and do not accept wildcard characters.
You click the Search button to find the first and then additional occurrences of the item for which you are searching.