Hello, I'm completely new to this whole story with Relay servers, I've been given task to set up Open source relay server with high authority. The scenario is: Isp that im currently working with wants a separate server to forward emails to it's destination. Mainly used for printers etc to send out notifications to users. Mail server is currently set up on a different server, running office 365. It has to be an Open Relay, I've been looking through many sources and still can't get the whole understanding of it. My question is how to set up Postfix on Ubuntu to act as ONLY open relay server on a separate server, and from my understanding how to point the Server 1 Office 365 to send mail through the relay server, which then will deliver mail to it's destination. I know Open relay is bad for spammers, but i believe there's settings in postfix to allow what networks are allowed to relay emails through it. Need more information? Feel free to ask me! Thanks for help!