I am working on a project that has us migrating approximately 2,400 mailboxes from Exchange 2003 to the New Office 365 (Wave 15). As you are probably aware it is not possible to install an Exchange 2013 server into an Exchange Organization that has Exchange 2003 servers, here is a link to the supported scenarios, http://technet.microsoft.com/en-us/library/hh534377(v=exchg.150).aspx So we went with the next option, using an Exchange 2010 Service Pack 3 Hybrid Server. We were able to get Hybrid installed along with Identity Federation setup with DirSync and Active Directory Federation Services (ADFS). We had verified Single SignOn as well as mail flow between on-premises and Office 365 and did a mailbox migration for a mailbox we created on the Exchange 2010 Hybrid server to Office 365. Everything was going smoothly.

Next step, we attempted to migrate a mailbox directly from the Exchange 2003 server to Office 365. First attempt was met with a failure on corrupt item count being exceeded. Easy enough, we used PowerShell to submit the Move Request and increased the BadItemLimit to 25. Well this migration failed as well, after reviewing the Migration log more closely it appeared that no successful items were migrated, the first 25 items attempted to be migrated were failed with corruption. Ok, maybe this is a messed up mailbox (it was a test mailbox that has been around for a while) again back to PowerShell and set the BadItemLimit to Unlimited. Failed again! Now I began researching and reaching out to my fellow MVP’s and my Microsoft Contacts. Long story short here is I found this to be somewhat of a known issue, you cannot migrate from Exchange 2003 directly to Office 365 even when using a supported scenario with a Exchange 2010 SP3 Hybrid Server. The only way that is currently available to get a mailbox migrated from Exchange 2003 to Office 365 is to do a dual hop; Exchange 2003 migrated to Exchange 2010 and then migrate to Office 365.

We tested this out and it the dual hop migrations completed just fine. While this is not ideal at all it does have one small benefit. Migrating from Exchange 2003 requires an offline migration, meaning the user cannot access their mailbox while it is being migrated. When we migrate from Exchange 2010 to Office 365 this is an online move, meaning the end user can be using Outlook or OWA to access their mailbox while it is being migrated. This small benefit allows for the downtime migration, from Exchange 2003 to Exchange 2010 to be done over LAN speeds and thus the downtime is shorter. Once the mailbox is located on Exchange 2010, the user can access the mailbox while we conduct the Exchange 2010 to Office 365 migration over the internet. Small victory! But this method does require more administrative overhead, end user communication and additional storage on the Exchange 2010 server to temporarily host the mailboxes while in transit from 2003 to Office 365. Our plan is to migrate user mailboxes in batches, moving a group from 2003 to 2010 the immediately to Office 365. This will minimize the additional storage on the Exchange 2010 server versus migrating all mailboxes first to 2010 and then to Office 365.

One decision we are still discussing is how to handle mobile devices. We are thinking about only touching, or having the users reconfigure the devices once, after the final migration to Office 365. Again still working on this, but we feel the phones might be “offline” for about a day or so. We will be talking to the business about this decision.

We did submit a Support Request via Office 365 to also validate the need for two hops in this scenario. Support did verify that right now this is the only way to migrate a mailbox from Exchange 2003 to Office 365 Wave 15. Support did ask us to run another migration from Exchange 2003 to Office 365 directly with some additional logging to assist them in gathering information and looking for a possible fix to enable direct migrations. I will keep monitoring this and if a solution becomes available I will either update this post or more likely create a new blog post.

I have also request that the link that I shared earlier in this post be updated to have a note that two hops are needed to migrate from Exchange 2003 to Office 365. Hopefully this gets updated soon.

UPDATED: We received the below information from Microsoft Support:

 We have been working with the backend teams on the offline mailbox move issues between Exchange 2003 to O365 via Exchange 2010 hybrid.

We understand that the fix is being rolled up rigorously to mitigate this issue and the problem should be fixed in the next 10days. I will keep you posted once the rollout have been completed.

Another issue that we ran into as part of this project is that the client is primarily using Outlook 2007 as their client. They did not enable RPC Over HTTP in Exchange 2003 (now called Outlook Anywhere) so the Outlook client did not have the checkmark set for Outlook Anywhere set:

(The above picture is from Outlook 2013 but is very similar in other Outlook versions)

This prevented the Outlook client from being Auto-configured for Office 365 after the migration completed. If we created a new Outlook profile it Auto-configured just fine and connected to the mailbox in Office 365.

What we found during testing is that we needed to enable this checkbox prior to Outlook being launched for the first time after the final Office 365 migration. Group Policy to the rescue, we added the Outlook GPO ADM and were able to configure a GPO to turn on (checkmark) the Outlook Anywhere feature in the Outlook client and this solved the issue.