Standard of SMTP. Test Deliver: Title & Messenger: Best Good For You.
Because of private server was not registered with major anti-spam organizations. I can't register. Unlimited SMTP cannot send inbox to popular email providers like: Gmail, AOL, Outlook, Yahoo...etc
+ Yahoo, Aol ( Spam )
+ Yandex ( Inbox )
+ 126.com ( Inbox or Spam )

+ Inbox Domain Mail don't have a system to filter mail, fight spam, Block ads, Block phishing mails