Setup self-hosted Smarthost to send mail to two hosts in parallel

[Arlesterc]

I am looking for a way to setup a self-hosted SmartHost that would let me receive email at two separate hosts in parallel. So if somebody sends an email to us it would go to two different hosts at the same time - I don't want forwarding. I understand that Postfix Relay Host would be one way to accomplish this. However I have not found any good docs on how to do that. If someone could let me know if Postfix Relay Host would accomplish what I want and if it does provide a link/instructions of how to set that up would be appreciated. Please note the solution doesn't have to be Postfix. Any setup that I can self-host that would be of interest to me.

Thanks in advance for any assistance with this.