Of course, you'll need an easy way to know when these people are included in these spaces so that you don't accidentally share confidential information. You'll see some areas in those spaces highlighted, like the border, message background, and icon in the message area and their email addresses.

external space participants

Your company can apply policies to restrict you from inviting people from outside your organization and prevent you from joining spaces owned by another organization. You'll get a message letting you know in these cases.