Hi,
I have a server (SMTP server) that NPM shows Down node, but I can ping in the NPM server (command line).
Are there any firewalls or IPS systems between the Orion NPM server and the SMTP server? They may not like the ICMP payload and could be dropping the packet. Under "Settings -> Polling Settings -> Network -> ICMP Data" you can modify the ICMP payload.
I already change that data to null: