Exchange 2016 on-prem migration to O365 RRS feed

  • Question

  • I'm learning the migration but no test environment.  Have read some articles and watched some videos.  But got some conflicted information.  Hope someone can ask those simple questions.

    1. where should I run HCW from?  I think I can start from on-prem EAC, hybrid, setup.  I think I also can login to office 365 admin portal and go to Exchange, hybrid then run from there?  Or go to to download then install. If I can install from either will they give me the same version?  My Exchange 2016 on-prem is on CU13, not very current.

    2. I heard that I can run multiple Hybrid agents.  I assume it's for HA purpose.  What function will need such HA?  I thought HCW just help create connections and trust between online and on-prem.  Once done what else it will do ongoing?  If I want want such HA should I just run HCW on another server?  

    3. When running HCW for what function or purpose should I select "Enable centralized mail transport" option?

    4. Will HCW automatically enable MRSProxy on a Exchange server or I need to do it manually?  Can I or should I enable MRSProxy on multiple servers?  Will mailbox move involve the server running Hybrid agent?

    5. After a mailboxes moved from on-prem to online I think the mailbox type will change to "Office365" under Recipient, Mailboxes, correct?  One article said it will disappear from Mailbox and show up under Contact as a mail user.  Another article said it will show up as Mail user under Contact but you have to run a few PS cmdlets to change its attributes to make it show up as Office 365 under Mailboxes.  Very confusing.

    6. From O365 EAC can I see mailboxes in on-prem Exchange server?  If so what type is it, mail user or contact?  What will it be if I moved it back from online to on-prem?  No show or mail user or contact?


    Saturday, July 20, 2019 7:48 PM

All replies

  • It is not that difficult. You can run HCW from on premise Exchange and you already have credentials for o365 portal.

    The wizard will let you go through some settings asking you the fqdn of the server which you can choose your externalwebmailaddress that will also be used for MRS. (eg. You will have to select from the exchange certificates to use for smtp (pop/imap) etc and personally you can avoid centralized loggin if you can)i tried to enable centralized logging but it can create looping as all emails from o365 try to come back to exchange server again. HCW will also copy some configuration from on prem to o365.

    The mailbox after moving to o365 will become user mailbox in o365 and mail user in exchange.

    Similarly you can see on prem mailbox on o365 as mail user (but under contacts). Online to onprem will restore them to original look but you can choose a different database on exchange

    Thanks & Regards Ramandeep Singh

    Sunday, July 21, 2019 6:11 AM
  • Thanks for the answers but want to clarify.  

    1. mailbox moved from on-prem to O365.  Where will it be under Mailboxes or Contacts?  I thought it will be showing as "Office 365"  under Mailboxes not mail user under Contacts.  Can you verify?

    2. Are you saying HCW will enable MRS Proxy on the server I chose during HCW installation?

    3. Some article said that I need to download HCW from MS which will be the latest version.  If using the install from on-prem EAC or online office 365 admin portal it might not be the latest version.  Is that true?

    4. After HCW installation and assume there will be no further change for Exchange on-prem do I still need HCW server?  Some articles said I should have multiple HCW agent?  What does HCW agent do?  Why do I need multiple HCW agents?  If for HA purpose how does the load get balanced among all agents?


    Monday, July 22, 2019 5:14 AM
  • I will answer your questions based on your original post:

    1. Each source is fine, you'll get the latest version of the HCW. Exchange 2016 CU13 is the latest version, it will be no problem to run HCW on it.

    2. The Hybrid Agent supports free/busy and mailbox migrations; mail flow, directory synchronization, and other hybrid features are not included.

    You have two options for Multi Agent Deployment.

    3. It depends on your actual mail routing, you could simply understand the "centralized" as letting the on-premise server decide the routing.

    For details, see Transport routing in Exchange hybrid deployments

    4. We often do this when migrating the mailbox, you need to manually enable it on on-premises Exchange server, it should be the server you are using to create a remote endpoint, generally the server running the HCW.

    Yes, it will involve.

    5. It will show as "Office 365 mailbox" in on-premise EAC.

    6. No, you cannot see them unless you put their on-premise users accounts in an OU synced with Azure AD. If the users have been synced to cloud and are not assigned licenses, you could only find them in "Office 365 portal -> Active users".


    Manu Meng

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    Monday, July 22, 2019 11:14 AM
  • Hi Manu,

      I have a few more questions.  

    1. Once ran HCW and there is no change on on-prem side I guess there is no need to re-run HCW again, correct?

    2. I assume that HCW installation also installs a HCW agent on the same server.  I think there is download for newer version of HCW agent.  If my HCW server was installed with an older version can I still install the newer version of HCW agent on another server for HA purpose?  Or I need to upgrade the one on HCW server?

    3. Assuming AAD Connect synced all users to cloud and I migrated John Doe to Office 365 but assigned Office 365 license only to the migrated user (John Doe) how can he send email to those on-prem because they are showing as "Active users", not a mail contact user?  I 

    4. related to question 3.  To let John Doe see on-prem email users should I 1) AAD Connect sync all users to the cloud prior to migration 2)assign Office 365 license to all of them, therefor they became Contacts in Office 365 3) after John Doe migrated he will see on-prem users as Contacts in his GAL.  Am I right?

    Thanks in advance.

    Monday, July 22, 2019 10:18 PM
  • A1: Yes, we don't need to run it again unless you get an error during the setup process.

    A2: You'd better update to the latest version. It is always recommended to do like this.

    A3: In your case, those Active users' mailboxes are located in on-premises Exchange server, right?

    Then mail between on-premises mailbox and O365 mailbox will be routed through the connectors created by running HCW.


    1) Yes.

    2) After the mailbox migration is completed, you could assign license to the migrated users, then they'll become mailbox account, not Contacts.

    3) No, it will display in the All users list, not Contacts.


    Manu Meng

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    Wednesday, July 24, 2019 10:41 AM
  • Just checking in to see if above information was helpful. Please let us know if you would like further assistance.


    Manu Meng

    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact

    Friday, July 26, 2019 9:43 AM