016-781 is absolutley no connection, so if the IP of the server is right along with the port. then it can only be the gateway or a proxy error.
I would have to assume an internal mail server since you are using port 25, because nobody uses that anymore due to security.
I'm trying to configure my email server, but nothing seems to work. I get the error 016-781.
I'm using the correct settings for my email server . port 25, correct password in smtp auth and SSL/TLS encryption none.
I'm also using the exact same settings in another xerox fax (xerox 3225) and everything is working fine there...
I tried using 18.104.22.168 as a secondary DNS and IPV4 as mentioned in some older replies, but still nothing..