Email flows from Office 365 to on prem and back to Office 365

Dear EE

I recently changed my domain’s MX to point to EOP. Mail flow is working to my 365 and on prem mailboxes fine however when emailing a 365 mailbox ,the email goes to EOP then on prem which routes it back to EOP. In 365 I set my accepted domains to authoritative however the result is the same so I set them back to internal relay. Please help. In my on premise org those domains are set to authoritative.

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Vasil Michev (MVP)Commented:
How long did you wait after setting the domain to authoritative? Do you have Centralized mail transport enabled? Does this happen for all users or only some?

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TTAF4Author Commented:
I waited  for a few minutes. Paul from also seems to think that I have centralized mail transport enabled. How do I go about checking that? I wasn't the one that ran the HCW initially. I have several vanity domains. One of them is called This was a test domain that I created. The MX for this domain also points to EOP. This domain is currently set to authoritative but even when it was set to internal relay email flowed perfectly.

Vasil Michev (MVP)Commented:
Simply rerun the HCW, it will show you whether it's enabled and you can quickly disable it.
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TTAF4Author Commented:
Will re-running the HCW cause an interruption in mail flow? Sorry for the many questions.
Vasil Michev (MVP)Commented:
Only if you change things :)
TTAF4Author Commented:
turns out Centralized mail transport  was enabled.
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