These are the SMTP Settings you can use below with eM Client.
SMTP
Port 587 = Force usage of SSL/TLS
Port 465 = Use SSL/TLS on special port (legacy)
Port 25 = Use SSL/TLS if available
If you don’t have any luck with sending with any of the above SMTP settings, then suggest if you have a current active paid Pro, Personal or Business version, to go to the VIP Support page and login and lodge a support ticket.
I see too there is another user @nyxis also having problems trying to send mail via QQ.com getting (Unable to connect to server) with “no optionally installed firewall / security, antivirus program or vpn”. So might be something specific with that particular smtp server.