All outgoing email to go to one intermediate mx server

[csac_it]

Ironport C100v email security, on-prem

Transitioning to cloud service

From the Ironport, rather than send outgoing email directly to recipient mx servers, I want all emails to first go to the FQDN for the cloud service for further processing, and then be sent on from there.

There is an SMTP route for our domain that points to our internal Exchange server. I think if I put the cloud FQDN in the default 'All other domains' SMTP route, that will send anything that is not specifically for our domain (i.e. all outgoing) to this external server.

Do I have that right? Thanks.

[Ken Stieers]

Yes.
Be aware that if you're using DANE for any of your recipients, that won't be in play any more unless wherever you send the mail supports DANE.
Make sure to update SPF, DKIM, DMARC
And I'd test with a domain first... say gmail, and make sure it looks right/passes all the deliverability tests before you throw all mail to the cloud sender.