Access old Exchage after migration to 365

New Contributor

Hi all

So I have migrated from Exchange OnPrem to Exchange Online.

Before migration I have taken a snapshot from the Exchange server, just in case.

Now, there is a user who claims that some of her contacts vanished during the migration. So I booted up the backup Exchange and tried logging into the OWA to see if I can find some cantacts there. However, when trying the OWA,  using the localhost url I get redirected to the online Outlook. Obviously the Exchange server recognizes soemwhere in the AD that we have migrated.


So my question:

How do I access the old information on the OnPrem Exchange Server if I did not think of keeping a backup of the DC?

8 Replies

This is probably occurring because the account you are using has the targetaddress attribute pointing to EXO. I don't have any answers on how you get around that though. Depending on how mail is flowing and where autodiscover is pointing, the targetaddress attribute may be critical

@Dan Snape 
Thanks for your reply

Do you at least have the information of the flow?

Say, first it checks DNS for the autodiscover, then it checks the autodiscover and checks to which server it points, then it looks at xyz etc.

If you know the answer it would also be helpful to hear what happens if it doesn't find the autodiscover or any other file along the way?

I do want to point out again that I attempted to login straight via the OWA on the (copy of the) Exchange Server itself, using "localhost" as the url. This server is supposed to be unaware of the migration, as it is a snapshot from before. So it doesn't really make sense to me that it would be looking for an autodiscover, which is used by a email-client to locate the server. The only thing it sould be checking is the username and password, which it is supposed to get from the DC

Thanks again for trying

If mail is flowing via the on prem Exchange (including anything being relayed), messages will be redirected as per the targetaddress attribute. This is the same for autodiscover. If mail is flowing directly to EXO, no on-premises apps or devices are relaying via on-premises Exchange, and autodiscover is pointing to EXO, then it's not a critical attribute.


For your access to the EAC, the OWA/ECP will check the value of the targetaddress attribute on the user AD object and redirect according to that value.

Wow, thanks so much for that
when changing the info of the targetaddress atribute in AD I managed logging into the local OWA of the old exchange server
however now I get a different error
We couldn't find a mailbox for this recipient. Either they don't have a mailbox or don't have a license assigned
Any thought on this, as this is the server as it was before migration there definitely is a mailbox? Where would it look for a license?
That one I'm not sure of. I would guess this is because of the recipient and recipient type details in AD that has different values depending on the location of the mailbox. If you are trying to log directly into the mailbox via OWA, these will need to have a value indicating the mailbox is on-prem. This blog has some details
Once the mailbox is migrated to O365, the OnPrem mailbox is converted to Remote mailbox.
There is no data available in the OnPrem remote mailbox, so this entire drill to login to OWA will have no benefit.

Don't make any changes to the target address as this will break client connectivity of the end user. And just to add here you cannot login to OWA because the user mailbox is not present OnPrem and that's why you are getting this error.

So you should communicate it to the end user that all the contacts in his mailbox were migrated.

The once that are missing were probably created in some pst file or some offline format and hence he cannot see them right now.

Thanks for your reply.
Me think you have missed an important part in the question
BERORE making the migration I have taken a snapshot of the Exchange server. It is on that snapshot, which has no knowledge of the migration, that I am trying to access the OWA.
So, you are definitely right about the mailbox not being available OnPrem, but an old copy should still be available on the old snapshot. The issue is only conviencing the server to allow access.
Changing the targetaddress atribute in AD allowed me to actually log in to the OWA, the server just claimed there was no license.

You did help me forward though. You say that once migrated the mailbox is registered as being remote. I assume that registration happens in the AD. Could you tell be what atribute is edited to flag the box as remote? Maybe if I will set that back to local I will be able to access the box on the old OWA.

I realize that changing the atribute in the AD has a direct effect on the current existing box. Obviuously I will change those settings back, once I have exported the data I need. Eventually, if I see that it takes longer than expected I might set up a closed envirnment in which I will put a copy of the DC together with the old Exchange server and than make the changes there.

Thanks for your 2 cents
Using Exchange Snapshots is not recommended and it wont help either. But if you still want to know the remote mailbox attribute it will be msExchRecipientTypeDetails set to “2147483648" in adsiedit.msc

If you have backup of the previous edb file then I will recommend you to mount it as a Recovery Database. Create a new test user OnPrem and you can create a New-MailboxRestoreRequest to move the data that was present in users mailbox when the backup was taken (Now in your recovery database) to the new test mailbox that you created.

Post that you can take a pst export of this data and share it with the user or login to the new test user mailbox and validate it yourself.