We've been directed to add an inbound and outbound mail relay (MX) in front of our existing Zimbra install. From an inbound perspective this is no problem. We'll be using Postfix for the relay system and will have it accept all mail and pass it on to Zimbra.
Outbound is where my question lies. I see in the admin console that there is a setting in the servers section for "Relay MTA for external delivery". Do I simply need to set this value to the new relay system and restart Zimbra? Will that have all mail be sent out through the relay. Do I also need to remove the setting for the webmail MTA hostname?