I am setting up a forum that CAN NOT be viewed by the outside public. Only registered members will be allowed to read and contribute posts.
And, if possible, members should only be able to join via invitation.

I would like to know what are all the steps and admin/config./host settings, etc. necessary to accomplish that?
(Or, as much of that, as possible.)

Thanks!

You can add new rule in access masks : Guest Access Mask : set all value to false and apply this mask for Guest.

Thanks for that tip.

I see I can also disable new users from registering, and force all users to log in before viewing any content on the page, through the host settings.

Is there any way to guarantee that search engines won't index the content?

Search engines can't index a forum if there is no permission to that forum for guest.

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