Sunday, 14 August 2016

Office 365 & Exchange Migration Split Brain AutoDiscover Workaround

I’ve just migrated an Exchange 2010 installation to Office 365 using the “cut over” migration method. As it was a small deployment I did not go through the exact process documented by Microsoft, instead I did a PST export/import migration. For this, it created an interesting problem in regards to name resolution for clients in the domain. Clients would successfully do an Autodiscover, but the internal DNS would continue to point users to the old Autodiscover service on the Exchange Server.

The following changes were made to prevent Active Directory resolving the old Autodiscover service;

·      Edited the “HomeMDB” attribute from ADSI Edit (Configuration)
·      Disabled (deleted) the Mailbox from Exchange
·      Recreate the Outlook profiles for each user

Remove the HomeMDB Attribute using ADSI Edit

Connect to ADSI Edit, and connect to the Configuration container and find the Microsoft System Attendant at the following path.

N=Configuration,CN=Services,CN=Microsoft Exchange, CN= "OU", CN=Administrative Groups,CN= Exchange Administrative Group, CN=Servers, CN=EXCH", CN=Microsoft System Attendant

Simply clear out the value in this attribute until it looks like this.


Disable the Exchange Mailbox (Delete the mailbox without deleting the user)

From the Exchange Management Console, browse to Recipient Configuration/Users, select the User and then choose the Disable option.


If you select the Disable option, the Active Directory user object will remain. The Exchange Mailbox is not actually deleted from the Mailbox Database until the next purge is carried out, which is determined by your Retention Policy.


Although this work around works fine in a small environment, it may not be so straight forward in a more complex deployment. It is possible to configure Autodiscover redirection if required.

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