By default, any person with an e-mail address can be invited to work on a model package or project.
If activated in the Team Server, inviting people may be limited to existing users and user groups with the Designer role. It means that you cannot invite people that do not (yet) exist in the Team Server and existing users who do not have the Designer role. The limitation can be (de)activated in the Team Server settings by users with the System Administrator role.
If the limitation is active, and (one or more of) the e-mail address(es) you have entered in Enterprise Studio does not belong to an existing user or belongs to an existing user who does not have the Designer role, a message will be shown below the entered e-mail address(es), and the Invite button is deactivated. The person's initials are not shown, instead, an exclamation mark is shown in red.
If one or more of the e-mail addresses when inviting people via the Team Server does not belong to an existing user or belongs to an existing user who does not have the Designer role, an error message will appear after clicking the Invite button. The invitation will not be sent.