**This blog is based on Exchange 2010 SP1 and not using the Hybrid configuration wizard e.g. SP2**
I’ve had a few customers in the last few weeks ask me how autodiscover works for Office 365 so thought i’d write a post to try and help! (please see my other post for the namespaces required, as the correct autodiscover records will need to be created in DNS for on-premise and Office 365)
As you probably already know, Exchange 2010 includes a service called the autodiscover service, this service allows an Outlook profile to be automatically configured when using Outlook 2007, 2010 or a Windows mobile 6.1 or later device. The autodiscover service uses a user’s email address and password to automatically configure a user profile. This profile can be configured whether the mailbox is located on-premise or in O365 (for more detailed information about the autodiscover service please the published white paper on TechNet).
For on-premise users to use the autodiscover service (where a user’s mailbox resides on-premise) there needs to be an A host record (other options are available, see the white paper ) created in external DNS that points to the externally facing IP address of the configured listener on TMG for example(for more details on publishing Exchange 2010 with UAG and TMG please see the following white paper - http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=8946)
For user’s who have a mailbox located in O365 there needs to be a CNAME record created for the service address space office365.company.com that points to autodiscover.outlook.com.
Example – autodiscover.office365.company.com --> autodiscover.outlook.com
When an on-premise mailbox is migrated to O365 their on-premise TargetAddress attribute will be updated to point to office365.company.com service namespace. Therefore when a user’s mailbox has been migrated to Office365 and Outlook attempts to autodiscover, Exchange will return the TargetAddress back to the user and Outlook will then lookup the autodiscover service at office365.company(which in turn points to O365) and will create the profile. See the diagram below for the process flow.
Note: That when a mailbox is migrated to O365 using rich coexistence there is no outlook reconfiguration or OST resync required after mailbox migration. Migrating mailboxes using rich coexistence supports full fidelity mailbox migrations.
Written by Daniel Kenyon-Smith