I do a lot of Exchange Online migrations. I’m not really sure how many I have done, but I would guess the number is between 50 and 100 over the last 3 years. Over 90% of those migrations have been Hybrid. In fact, I’m pretty sure only one or two of those migrations have not been hybrid. Recently I had occasion to do a staged migration. I’d like to go through that process and discuss why I ended up making the choices I did.

This staged migration was for a small company that was running Exchange 2003 on-premises. The original plan was to do a hybrid migration for this customer as well. When I arrived onsite to start the migration I found they had an Exchange 2000 server that was also an Exchange 2000 domain controller running in their environment. At some point in the distant past Exchange 2000 was partially uninstalled from this server. As I dove a little deeper into this server, it appeared that the recipient policies for Exchange had not been properly migrated to the Exchange 2003 server. This meant that the old Exchange 2000 server had to be on for the customers Exchange organization to do much of anything at all.

At this point, I decided that a Hybrid migration was not going to work. You cannot install Exchange 2010 into an AD domain that has Exchange 2000 servers, and spending a bunch of time trying to fix and/or properly uninstall the Exchange 2000 server would put this migration too far behind schedule. In addition, the customer had a requirement to use DirSync to support a compliance application. The requirement for DirSync, and the inability to installed Exchange 2010 left me with only one option; the staged migration.

The Exchange Online staged migration is specific type of migration that has specific requirements and benefits. Besides the hybrid migration (and I suppose multi-forest hybrid migrations), it is the only migration type that supports DirSync. The staged migration can only be sourced from an Exchange 2003 or 2007, and uses Outlook Anywhere to copy the data instead of MRS that is used with hybrid migrations. Staged migrations do not provide the rich co-existence of hybrid migrations, but they do provide a unified GAL.

Here are the requirements, pros, and cons of the staged migration vs the hybrid migration.

Requirements:

1. Source server must be Exchange 2003 or 2007
2. DirSync must be installed
3. Outlook Anywhere must be enabled

Pros:

1. Easy setup (vs hybrid configuration)
2. Unified GAL

Cons:

1. No Free/Busy federation
2. No public folder migration path
3. Mailbox permissions don’t migrate