Hello, I had setup a vps where I followed the guideline on Perfect server - CentOS 7. Everything seems fine except the postfix where I can see there are some emails could not be delivered with the following errors in the mail log. I had the firewall in active with the port 25, 587, 993, 995 enabled. I also did the telnet on the port 25, 587, 993, 995 all working fine. Could this because of my server settings problem? Any suggestion?