Create shared mailbox on Hybrid environment - directly on O365 or onpremises then migrate it to O365

Brass Contributor



What is the recommended way to create shared mailboxes for a hybrid environment? There are some issues if you create them directly to O365 -


Create it onpremises then migrate it to O365 is the best practice?

24 Replies

Hi Carlos,


If you still have mailboxes on-premises and would like to have access to your shared mailboxes you should create on-premises and then migrate to Office 365.

Hi Nuno,


My mailbox is already migrated to O365 from a while a go, but tonight I tested creating to shared mailboxes. One directly on the cloud and the other on-premises (then migrated), after applying the full access permissions on both for my account only the second one is working (including auto mapping)


I was expecting that for both shared mailboxes to work, but apparently the ones created directly on the cloud have some issues with delegation.


So, I assume that create the shared mailboxes on-premises and then migratem is the best solution even if we have all of our user mailboxes migrated.



best response confirmed by Carlos Gomez (Brass Contributor)

Hi Carlos,


If you have an Hybrid, your autodiscover is pointing to your on-premises Exchange. If you create your Mailbox only in Cloud, your AD and Exchange does not have any propreties of that mailbox, that is the issue.


So, I asume that since AAD Connect does not support write-back (only password) then its better to have the objects created first on-premises then moved to O365 in order to avoud such situations.


Or is there a change that could help on this?



Hi Carlos,


You can create some Exchange objects on-premises manually to do that but if the mailbox has no data on it, just create a new one, it's faster.

What Nuno says is correct, but when you have migrated everything with the hyrbid your autodiscover will propably point towards Office 365 and you exchange hybrid server is just a exchange server for managing purposes. When this is the case the best thing to do is create the shared mailboxes online (just cloud only).

But if you still have users onprem and maybe some online then the method nuno told is the way to go. Also make sure the proxyaddress have (this is used for the automapping).

The method that works for me is:


1) create a user mailbox in OnPrem Exchange

2) move the user mailbox to office 365

3) Once move is completed, Convert to shared mailbox (either through EAC or EXO PS using set-mailbox -type shared cmd)

4) remove license as it is no longer needed for shared mailbox

5) Assign mailbox delegation to required users


This ensures the mailbox is known between both Exchange onprem and Exchange online realms and doesn't bypass the federation if it's created in the cloud originally. The only Exchange objects that should be recreated in the cloud for a hybrid deployment are DDGs since they can't sync through AAD Connect. Every other EX object should always be created in onprem realm and then synced to EXO via AAD Connect.


Hi Carlos,


Other way is creating the Shared Mailbox in On-prem and then migrate it to O365.


This will leave a contact in On-prem (for compatibility for non-migrated users) and the Shared Mailbox will live in O365.  



I currently:


  1. Create an AD account in a OU that syncs with 365.
  2. On my on-prem exchange, run a powershell command:
    enable-remotemailbox <name> -remoteroutingaddress <mailbox>@<company>
  3. Once 365 has synced, change the mailbox to shared.
  4. Back in Active Directory I change the attribute msExchRecipientTypeDetails to 34359738368 and msExchRemoteRecipientType to 100
Going to try this now. Looks like this is what I do for new users. step 3 and 4 is what I was needing to know for new shared mailboxes.
Hi Fermin
Did you try this method? Did it work? We're looking to find the same answer. Thanks!


We have Hybrid.

We always create user and mailbox on prem  then migrate to O365 .

We do this both for regular an shared mailbox.

Never had a problem.


In case regular mailbox is in o365 and needs to be converted to shared mailbox.

We migrate is to onprem convert to shared with the command and then migrate it back to O365.

Dont know if there is any other option?

Would be nice just to convert in O365 !



Hi David,


You can convert in Office 365 the shared mailbox on the Exchange Admin Center or Exchange Online Powershell. 


You do not need to migrate the mailbox to on-premises.



Are you shure that wont give any problems.


We dont have AD write back to onprem...


So i asume just login to exchange online and stet mailbox shared with powershell ? 





Hi David,


If you do not have AD write back the process is what you describe. Here is the support article with information

Ok Thanks


I had some hope ... 






Hello None None, 


I have a couple of question regarding your post. Your method for shared mailboxes in Hybrid environment.

  1. Can I just create the mailbox as shared from the beginning in on-prem exchange server?
  2. How do I create bulk shared mailboxes in the on-prem server?
  3. Can you clarify this, I researched that you need to import the .csv file into EMS, if that is the case, do you know of a way to create a .csv file template to import into EMS?

Please, let me know at your earliest convenience.



Thanks for these instructions.

Used them when I already had the shared mailbox created on the cloud and synced to on-premises AD.

Just ran the powershell command in the exchange console, changed the attributes and ran a delta sync cycle.



1 best response

Accepted Solutions
best response confirmed by Carlos Gomez (Brass Contributor)

Hi Carlos,


If you have an Hybrid, your autodiscover is pointing to your on-premises Exchange. If you create your Mailbox only in Cloud, your AD and Exchange does not have any propreties of that mailbox, that is the issue.


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