Cutover Migration from Exchange 2010 SP2 to Office 365

Hi Minesh,

For your concerns, I will answer the questions in turns.

Q: Can I use the Cutover migration method to migrate the contoso.com (110 mailboxes) and then a month later migrate fabrikam.com (440 mailboxes) Is this possible ???

A: Currently the scenario you described is not officially supported in a cutover migration. If you want to migrate user mailboxes to Office 365 in bulk and you have Exchange server 2010 installed, we recommended you deploy Exchange hybrid and use remote move to migrate them.

Q: According to Microsoft 2000 mailboxes can be migrated yet the Exchange online center can accommodate only 150 mailboxes ???

A: We can migrate a maximum of 2,000 mailboxes from your on-premises Exchange organization to Exchange Online using a cutover migration. However, Exchange Online processes up to N migration requests at one time, where N is the maximum number of concurrent migrations that the administrator specified when creating the migration endpoint used for the migration. By default, you can migrate up to 20 mailboxes at the same time until all the mailboxes in the on-premises organization have been migrated. Given the information, it may take times to create and migration 2000 user mailboxes, which is why we recommend you use cutover migration to migrate 150 users or less.

For more details, please refer to: Cutover Exchange migration.

Thanks,

Neo Yu

Hi Minesh,

I'll just elaborate on Neo's comment, to explain why such a migration is not recommended.

When migrating mailboxes, there are a few concerns to consider:

1. Mail-Flow:

Since you have two organizations, you would like them to be able to continue communicating with one another once Contoso is migrated.

This scenario, in a cutover migration, raises two issues-

First of all, as both organizations are hosted on the same Exchange server, you will have to consider mail routing- connectors, remote domains, etc. Your Exchange server believes he is authoritive for Contoso, and therefor will not forward Contoso mail items unless you create appropriate Send\Receive connectors.

The second issue would be the cutover migration behavior. This kind of migration only migrates data to Office 365, but does not deal with on-prem cleanup. This means, that once the migration is complete you will be left with legacy mailboxes on your Exchange server. Once again, this would be a mail-flow issue since your Exchange server will ignore connectors if a mailbox is found (messages will be delivered to on-prem mailbox). To overcome this, you would have to disable those mailboxes and create remote mailbox representation instead (or, simply a mail user) with a routing address that points to Office 365, according to the connectors from the step above. If you do so, keep in mind legacy addresses such as X500s as neglecting it would result in NDRs for you on-prem users.

2. Migration itself:

Cutover migration is designed as a one-time wonder. Assuming that you will be running directory synchronization, and given the size of your environment I believe you will- once migrated the first users using Cutover migration and activated sync- the cutover migration option will be blocked (grayed out). Leaving you with remote move as your best option.

3. User experience:

Using Cutover migration, user experience is not as good as using the Exchange remote move available to you on Exchange 2010sp2. User profiles are lost, permissions, free-busy access, and more.

If after all you still prefer not to run a full Hybrid, a solution I used for some of my clients is simply install AAD-Connect and enable the MRSproxy for Exchange remote move. In your case, you will also require send\receive connectors, therefor I would still recommend going by the book with a Hybrid solution, which considering all the above, size of your environment and options, would be the best solution- for your users, and for you as an IT administrator.

It might take some time to set up, but it will prove worthwhile. 

Regards,

Maor Bracha