how to Stop wpforo forum emails from going into the spam box?
This is not wpForo email. This is your website email sent by your WordPress installation. All emails are sent by WordPress, wpForo just provide a form for that, nothing else.
The 99% reasons of emails going to spam box is the FROM Email address and the sender server safety. The FROM EMail address should be safe and the hosting server should be trusted by Google. As far as I see your sender server is 000webhosting.io. This is a free webhost with a very bad reputation in Email Sending history. Most spammers use such servers for sending spams. So please don't blame wpForo and don't search solution in wpForo. wpForo doesn't have any relation to the emails in spam box. Just register a legal domain, install a WordPress in the legal domain with a good hosting server, then set the FROM Email in Dashboard > Forums > Settings > Email admin page a good email address with your domain, such as noreply@yourdomain.com . In this case the email should be trusted and delivered to inbox.