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Microsoft Working on Solutions to Remove On-Premises Exchange Server Requirements

During the Ignite session titled “Run Microsoft Exchange Hybrid for the long haul”, Microsoft has hinted at potential solutions to the problem that many customers face after migrating to Exchange Online.


One of the frustrating discoveries for a lot of customers is that moving your email to Office 365 doesn’t necessarily mean you can say goodbye to your on-premises Exchange servers. Even if you’ve used a hybrid configuration to get through the migration, and then removed the hybrid config at the end, you’ll still need to maintain an Exchange server on-premises for management purposes if you continue to use directory synchronization (which many customers do).

To be clear, it’s not the hybrid that creates the dependency of an on-premises server, it’s directory synchronization. Directory sync makes your on-premises Active Directory the source of authority for your directory information (users, groups, etc). It’s super convenient, providing same sign-on or single sign-on access to Office 365 services. But the catch is, you need to manage the user attributes (including email attributes) on-premises. And the only supported way to manage email attributes is using the Exchange management tools, which means you need an Exchange server.

There are some benefits to keeping an on-premises server though. Using it as a local SMTP service is handy, and if you leave the hybrid configuration in place it also provides you with the flexibility to off-board from Exchange Online in future if the need arises.

Still, customers who want to reduce their on-premises server footprint will always want the option to ditch Exchange. I’ve often thought that a lightweight “management appliance” might be able to do the job, something that can co-exist on the same server running the directory synchronization service as well. How feasible that idea is, I don’t know, but its encouraging to see that Microsoft is actively pursuing a solution to such a regular complaint.

h/t to Jetze Mellema for tweeting this info from the session

Paul is a Microsoft MVP for Office Servers and Services. He works as a consultant, writer, and trainer specializing in Office 365 and Exchange Server. Paul is a co-author of Office 365 for IT Pros and several other books, and is also a Pluralsight author.
Category: Blog


  1. Ejaz Ahmed says:

    Hello Paul,

    Having a lightweight tool to manage these four attributes or something which can coexist with directory synchronisation server will certainly be an attractive option for customers. Microsoft certainly thinking in the right direction.

  2. John Gaudio says:


    Using third party tools such as bititan and skykick , specifically cutover migrations leaves you with an unsupported Microsoft environment. My question is “what is the recommended way to create a supported environment after a cutover migration?” The 3rd party providers don’t have a solution and Microsoft wont help with an unsupported configuration. Leaves us holding the bag. There seems to be no easy way to decommission the Old On-premise server and create a supported environment. In some scenarios the old on-premise server needs to be decommissioned.


        • Then that’s been added after the migration I suspect, as Microsoft’s cutover migration method doesn’t work with directory sync in place.

          Yes, if you want directory sync, you need to retain the on-premises Exchange server to remain supported. That requirement should be identified early in the project planning.

          • Kristoffer Hansen says:

            I have done over 100 office 365 implementations for companies using dirsync and now ad connect installed before the cutover and migration. Just leave the msexchmailboxguid attribute out of the sync, migrate the mailboxes and do the cutover. Remove all traces of onprem autodiscover and later remove the exchange servers from AD manually (adsi edit). Its no problem at all, and in my opinion gives a faster, clean cutover. Outlook profile can easily be managed just by deploying a registry GPO “hack” to force a new profile creation on outlook startup. All attributes can easily be managed using ADUC.

            I am going to test reinstalling exchange to the same AD to get the management tools, should not be too much hassle i guess.

  3. Marc Kean says:

    You know we did exactly that, migrated mail to O365 with DirSync, the Exchange server on prem, i shut the Exchange server down at the end if the migration on purpose to prove that i could survive with it out. We just used a mix of AD users and computers MMC and PowerShell to edit the mail based user attributes in which the Exchange tools modify anyway. After all, all the information stored in the ‘directory’ in which you have full access to using AD or PowerShell.

  4. Brian says:

    I have an Exchange 2010 environment with 2 Exchange 2013 servers for a Hybrid setup, using AD Connect for directory synchronization. I would like to remove just the Exchange 2010 servers since our on-prem mailboxes are migrated to 365. My understanding is I need to keep the 2 Exchange 2013 servers. Guessing the ebook goes over the decommission process for those 2010 servers in our scenario?

    • Whether you need 1 or 2 Exchange 2013 servers is more a question of availability. If 100% of your mailboxes are in the cloud, mail routing goes directly to the cloud, and Autodiscover resolves to the cloud, then the main role that the on-prem server is providing is as a management/admin interface. So it depends how available you need that to be for your IT teams. Some customers get by just fine with 1 on-prem server in long-term Hybrid scenarios.

      If you’re adding or removing servers in a Hybrid scenario, and those servers are involved in some Hybrid functionality (e.g. mail flow, MRSproxy for mailbox moves, etc) a general rule is to re-run the HCW afterwards to adjust the config for the changed environment.

  5. Attila Rozgonyi says:

    Hello, we have a somewhat unique situation where 100% of mailboxes, distribution lists, public folders, etc. have been migrated to O365, so that there is nothing remaining in the on-prem 2010 exchange servers. We have a hybrid server and a separate DirSync server running AADConnect. To complicate matters, we are also doing a domain migration to a new forest. Whilst 100% of mailboxes have been migrated to O365, only 50% of the users have been migrated to the new domain. The legacy exchange & hybrid servers are in the old domain. My customer wants the old exchange servers & hybrid removed (but is happy to leave the DirSync server). A new Exchange 2013 server was installed into the new forest, but this does not know about the old forest or O365 mailboxes. Therefore, my concern is that if I remove the legacy exchange + hybrid servers, I will not be able to manage half of the mailboxes because the 2013 exchange server is in the other forest. Would I need to install a 2013 exchange server in both forests?

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