We've just installed a new Exchange 2016 server, working in co-existence with our Exchange 2010 server. We have the SMTP proxy working fine for inbound and outbound. I'm now changing the mail flow to go through the 2016 server. Inbound is working fine but when I change the outbound, the email never gets delivered. I have setup Exchange to use the UTM as a smart host, just as before in 2010 and have added the 2016 server as a relay on the UTM and changed the routing to use the 2016 server, instead of the 2010 one. I know the send connector in Exchange 2016 is working OK, as when I choose to deliver by mx record, rather than by smarthost, the emails are delivered. I am seeing some entries in the SMTP log about the message being moved to the work queue, so I know the mail is reaching the UTM.
Can anyone help?
Thanks in advance.
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