Unknown SMTP host: pdc1.nest.stpt.soft.net

Well, is this the exact same hostname you are giving on your command line?

Does this hostname resolve in DNS and/or the local hosts file, on the machine where this code is running?

(do you know how to use tools to resolve a hostname in DNS? depending on what kind of system you are running on, you would use "dig" or "host" or "nslookup" to just query DNS directly, and/or "ping" or "traceroute" or "tracert" etc. if you can't find one of the direct tools, since these secondary tools do the DNS lookup before continuing to try and connect)

Also if you are behind a proxy server and firewall, it may be that you can't resolve the given hostname in the internal DNS at all, because you're just supposed to let the proxy server handle it for you. In that case you'd have to find an SMTP server which you CAN resolve locally.