Smtp relays

Question

We migrated from Exchange on premise to Office 365. We had a Symantec SMTP gateway (out of service)which relayed mail from several applications to our partners outside the company. Each application came from a different username in our domain. We need to continue to send these email through a relay. One application's email needs to be hold at the relay for review before sending. I am looking for any suggestion on software or hardware to accomplish this relay. I have looked everywhere and all I find is services for email campaigns. The applications generate invoices and documents not surveys or mailings.
Thank you for any guidance you can give.
John

Answer 1

You can try creating a transport rule like this for message approval:

For more information, check Common message approval scenarios in Exchange Online

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