To enable or disable guest posting, you need either the moderator or operator role.

Normally, only people who are members of your campaign may post in the forums. However, it is possible to set up a forum to allow for guest posting - this may be useful if your campaign is set to invite only, so players can request an invite.

You can enable or disable guest posts in the forum details by visiting to the Forum Management page and expanding the forum with the edit icon on the right side, or by editing the specific forum.

Once you have found the editor for your forum, you can enable or disable guest posts by toggling the checkbox.