1. 11/27/2018 5:57 PM
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2. 11/27/2018 5:57 PM
THR2145
Why do we need to keep an Exchange Server on-premises when we move to the cloud?
Brian Reid (Office 365 MVP and Exchange MCM)
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3. What Is Identity Hybrid
We are all familiar with the idea of Exchange Hybrid
Exchange mailboxes for the organization are in Exchange Online and Exchange Server with a shared namespace, shared address book and free-busy coexistence etc.
As Exchange Server stores object attributes in Active Directory, we need to sync directories to Azure AD to support Exchange Online Hybrid
When all our mailboxes have moved to Exchange Online we still have a directory sync requirement, and therefore we have “Identity Hybrid”
Its all to do with “source of authority”

4. Identity Hybrid Azure Active Directory Exchange Online EXODS
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Identity Hybrid
Azure Active Directory
Exchange Online
EXODS
All Office 365 diagrams need a cloud
Exchange Server
Active Directory
AADConnect Server
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5. What happens if we uninstall our last Exchange Server
We still have Identity Hybrid – that is unrelated to our last Exchange Server
With directory sync in place (AADConnect) the majority of Azure AD attributes are read-only in Azure AD – they need to be changed in Active Directory
We now do not have a supported way to change these attributes, if we even know what these attributes are
We need to resort to ADSIEdit etc. and we don’t even have a good script engine to help with consistent and bulk edits

6. Attribute Considerations
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Attribute Considerations
Important Attributes
msExchMailboxGUID
msDsConsistencyGuid
proxyAddresses
Address Policies > not an attribute, but Exchange Server ensures uniqueness and consistency of proxyAddresses
legacyExchangeDN (and X500 addresses in proxyAddresses)
Exceptions to the rule
UserPrincipalName and Mobile Number
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7. 11/27/2018 5:57 PM
What Do I Really Need
Exchange Management Shell and Exchange Control Panel require an Exchange Server install
They do not require lots of disks and RAM
Therefore they are a "management server" and very easy to virtualize
Exchange tools update AD in a supported way
And there are nine attributes that write all the way back from Exchange directory (EXODS) to AD (need to configure this in AADConnect)
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8. So Can I Remove The Last Exchange Server
11/27/2018 5:57 PM
So Can I Remove The Last Exchange Server
Yes, if you remove directory synchronization first – this makes all the objects editable in the cloud and unrelated to Active Directory
But, an on-premises Exchange Server can act as a mail relay for all your on-premises applications and devices that need to send
So you might not want to – there are considerable benefits with directory synchronization
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9. What Do I Gain Accurate recipient and associated object management
Staying supported
Easier offboarding and mergers and acquisition scenarios
Easier to upgrade Exchange Server to latest version when all the server is doing is management roles
for the details we have covered here

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11/27/2018 5:57 PM
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11. 11/27/2018 5:57 PM
© Microsoft Corporation. All rights reserved. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.