Our emails to qq.com addresses get rejected and bounce.
Googling the error code, "Diagnostic-Code: smtp; 550 Connection frequency limited." it seems like a known issue with qq.com email addresses and many are facing the problem.
We currently use a Host Gator's VPS server as our mail server.
If you know a solution to this problem, whether it requires a migration to another server, or changing configurations on the current VPS server, please help!
Thank you and looking forward to your applications.