We are currently in a hybrid deployment of O365 with on-prem exchange 2010. We are having an issue getting an internal secondary domain through the barracuda spam filter. The email gets accepted but then rejected because we don't allow smtp relaying.
We are considering creating a smart host entry on the barracuda to accomplish our request. Would this be the best way to accomplish this without enabling smtp relaying?
local domain: domain.com
secondary domain: a domain.com
emails are coming in from MS O365 to the barracuda through a internal-relay domain
current internal exchange 2010 server uses a smart host relay to forward internal messages to the secondary domain.