No mail to the admin
Also please read this support topic:
It doesn't go just to my company mail. Don't know for other emails from our domain. The "from" was a company DL address. Tried with a gmail and worked - it sent an email to my gmail.
Changed the "from" to a gmail and still didn't send an email to my company email. Please advice.
The topic was useful, but didn't solve the issue ( https://wpforo.com/community/faq/not-receiving-automatic-replynotificationconfirmation-emails/#post-5344 )
You should not change FROM to gmail. From should have website domain name, otherwise it'll be traked as spam from Email Server Spam Blockers. It's already mentioned in the topic. This doesn't have any relation to wpForo, this is a general thing. The From Header email address should be with the server domain name email@example.com. This is the most safe way to play around spam blockers.