Does your platform allow us to set up a 3rd party outbound relay for the emails to our group?
Could you explain what that is? ?
If you want group messages forwarded to an external list (relay) that might be tricky to get past the address confirmation stage, unless your group upgrades to Premium and uses the Direct Add feature.
If you want messages from an external list (relay) to be posted into your group you probably need to use an email integration, and add the integration address as a recipient to the external list.