Hybrid Exchange Online Weird Routing.

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gbwelly

1263 posts

Uber Geek
+1 received by user: 776

#299280 25-Aug-2022 18:46

I've got experience with Exchange, I've got experience with Exchange Online. What I don't have a lot experience with is Hybrid Exchange.

I am moving to a new gateway provider who can deliver inbound mail directly into Exchange Online. It is working, however all mail is being routed from provider->EXO->On-Prem Exchange->EXO before it's delivered to the user, even though the mailbox is hosted on Exchange Online.

On Exchange Online under Accepted domains it is set to Authoritative

Can any Exchange Guru tell me why my mail is going on a tiki tour through on-prem?

dt

1152 posts

Uber Geek
+1 received by user: 371
Inactive user

#2961326 30-Aug-2022 21:36

did you figure this out? im in the discovery phases of figuring out what I need to do to turn off hybrid exchange server, all our mailboxes are in exchange online and all devices such as printers etc are relaying via exchange online as well

everything I find says it's because it was setup as 'hybrid' and something else to do with AD connect and on prem DC's. I just want all our on prem stuff gone but there's no clearly outlined process what you have to do to get rid of it all!

eluSiveNZ

192 posts

Master Geek
+1 received by user: 42

#2961341 30-Aug-2022 22:53

Sounds like your hybrid was configured to use Centralized Mail Transport (CMT)

You can turn this off pretty easily by re-running the HCW (Hybrid Configuration Wizard) but all depends on how this was configured initially.

eluSiveNZ

192 posts

Master Geek
+1 received by user: 42

#2961342 30-Aug-2022 22:56

dt:

did you figure this out? im in the discovery phases of figuring out what I need to do to turn off hybrid exchange server, all our mailboxes are in exchange online and all devices such as printers etc are relaying via exchange online as well

everything I find says it's because it was setup as 'hybrid' and something else to do with AD connect and on prem DC's. I just want all our on prem stuff gone but there's no clearly outlined process what you have to do to get rid of it all!

If you are syncing users from on prem AD to Azure via AADConnect you will need to keep an Exchange server installed.

Jogre

182 posts

Master Geek
+1 received by user: 40

#2962371 2-Sep-2022 15:07

eluSiveNZ:

dt:

did you figure this out? im in the discovery phases of figuring out what I need to do to turn off hybrid exchange server, all our mailboxes are in exchange online and all devices such as printers etc are relaying via exchange online as well

everything I find says it's because it was setup as 'hybrid' and something else to do with AD connect and on prem DC's. I just want all our on prem stuff gone but there's no clearly outlined process what you have to do to get rid of it all!

If you are syncing users from on prem AD to Azure via AADConnect you will need to keep an Exchange server installed.

Not quite true. You can offboard Exchange, you just need to (temporarily) turn off AAD Connect. How and when to decommission your on-premises Exchange servers in a hybrid deployment | Microsoft Docs

On-prem AD with AD Connect without on-prem Exchange is a supported topology with Microsoft, it is just the Exchange Product Group that doesn't know about managing AD Attributes using the Attribute Editor (ADUC Advanced Features menu) instead of ADSI Edit. AAD Support, EXO Support both support this topology.

You need to be very careful (i.e. make sure you have AD Recycle Bin enabled) when you uninstall the last Exchange server as if you don't follow the guides, you'll dump all your cloud accounts and mailboxes when the next sync runs. If you want to keep mail attributes on your On-prem objects, you can extend the schema back to AD afterwards if your mail attributes are gone which is handy for dynamic distros using custom Exchange attributes.

Jono Green

Microsoft New Zealand