In the background information page on firewalls <https://community.tp-link.com/en/home/stories/detail/255> TP_TechWriter describes the Firewalls and comments that SPI is enabled by default, and DoS "Y

I have a mailserver in my network and a fixed IP. The ports on the server report that they are listening, but another machine on the internal network reports (through nmap) that the host is down. I am