How can I improve message delivering?

I want to ensure messaging is delivered/received at all cost (At least from my end). So I decided to give SMTP a boost by doing some QoS (Quality of Service), I created several traffic shaping classes like this:

high is used for SMTP and DNS
normal is for used for Web Proxy
low is for used for controlling applications using Web Proxy, which tend to generate lots of traffic, like Mega

IMO (Correct me if I’m wrong please), by prioritizing this two protocols, messages should get delivered more quickly, as more bandwidth will be spare for them, as long as max message size (10 MB) divided by this assigned bandwidth (167 Kbps) don’t go beyond time declared on this three Postfix configuration parameters:

  • smtp_data_done_timeout (default: 600s)
  • smtp_data_init_timeout (default: 120s)
  • smtp_data_xfer_timeout (default: 180s)

Problem is that class High on traffic shaping remains unused (Checked using fireqos status red1-out and fireqos status red1-in) This are my Firewall Rules for Traffic Shaping:


Also, how can I increase above configuration parameters for Postfix? My bandwidth is 1612 Kbps for download (2048 Kbps theoretical ) and 335 Kbps (512 Kbps theoretical ), so increasing this values may also help message delivering.

Thanks in advance