When planning your migration of Exchange to Office 365, you’ll find there are several options available to you. Should you use a third-party tool to perform the migration? Should you use the cutover or staged migration technologies built into Office 365? Or, should you perform a Hybrid migration?
When you migrate mailboxes using Exchange Hybrid, you get the best end-user experience and the most straightforward experience as an IT admin.
A Hybrid migration allows you to move the mailbox, not just copy the emails, contacts and calendar items to Office 365. It uses the same underlying technology you might have used in the past when you’ve upgraded between Exchange versions, meaning that Outlook clients don’t need to be manually re-configured or re-download their cached mailbox data.
And, just like on-premises mailbox moves, you can perform an initial synchronization of the mailbox to Office 365 behind the scenes prior to completing the migration and switching them over – and even migrate the mailbox back to on-premises if you need to.
Hybrid has a reputation for being hard
A simple process for IT and a great experience for users mean that it should be an easy choice when it comes to Exchange Hybrid. For many organizations, it isn’t.
Hybrid has a reputation for being difficult to implement and get right. A traditional Exchange Hybrid implementation includes more than just the mailbox moves – it also includes planning for long-term co-existence.
One option in the Hybrid Configuration Wizard that’s been around for a couple of years now is the Minimal Hybrid Configuration option. If you’ve read up on Hybrid migrations in the past and haven’t heard much about minimal Hybrid, then you’ll be pleased to know that it’s one of the foundations for simplifying the Hybrid set-up process.
Figure 1: Choosing the Minimal Hybrid Configuration option.
When you run the Hybrid Configuration wizard today, you’ll see the option immediately to choose Minimal Hybrid – and it’s suggested as the recommended option. But how does it make a Hybrid migration easier?
Minimal Hybrid pairs well with new Hybrid capabilities
If you’ve read Dominik’s recent article Hybrid Exchange: Making it easier and faster to move to the cloud, then you’ll be aware that the Hybrid Agent will make one of the most complex aspects for enabling Exchange Hybrid much easier for most organizations.
By far and away the most complex aspect to Exchange Hybrid often is publishing Exchange Server to the internet in a way that works well for Hybrid migrations. The Hybrid agent takes away the requirement to do this. Install the Hybrid Agent, and (put simply) Office 365 can migrate mailboxes from on-premises without you needing to change any inbound firewall rules, reconfigure load balancers or reverse proxies or change Exchange URLs and SSL certificates.
What Minimal Hybrid and the new Hybrid Agent don’t do
Minimal Hybrid is focused on making the migration easier and simpler, not long-term co-existence. It doesn’t configure several Exchange Hybrid aspects that the full Hybrid configuration does, including:
- Free/Busy sharing – the ability to see people’s availability when some are on-premises and some are in Office 365.
- Secure Mail flow – a core aspect of Full Hybrid, secure mail ensures that “Exchange email” looks like “Exchange email”. Internal out of office auto-replies, voting messages, and the ability to use functionality like Centralized Transport (where all email in and out of Office 365 flows through your on-premises Exchange Servers).
- Lesser used functionality, like cross-premises eDiscovery and full integration into service like Skype for Business Online or Teams for on-premises mailboxes.
You’ll also expect not to configure some advanced functionality, like the ability to grant full access permissions to mailboxes, cross-premises, send-as or send on behalf of rights and granular delegated permissions on Calendars. After all, should you need that functionality for long-term Hybrid, capabilities such as secure mail flow and availability will also be key.
Full Hybrid with the Hybrid Agent
Therefore, whilst the Hybrid Agent is a crucial, useful new development, it doesn’t absolve organizations of all the tasks they’ll need to perform for a long-term Hybrid or full Hybrid implementation.
If you use the Hybrid Agent, although you won’t need to publish Exchange Server for your Hybrid migration, and free/busy sharing, you will still need to publish SMTP – both inbound to your Exchange Servers and outbound to Office 365. This is often a complex step for organizations who’ve traditionally used an on-premises (or cloud-based) spam and malware blocking appliance rather than publish their Exchange Servers.
Making the decision between Minimal and Full Hybrid
As you’ll see, migration-only scenarios pair well with the Hybrid Agent and Microsoft are clearly banking on Minimal Hybrid with the Hybrid Agent being key to making migrations much easier.
As the decision isn’t just about the migration itself, we’ve put together a simple table to help you make the decision between minimal and full Hybrid:
| I need…. | Use |
| To migrate all mailboxes to the cloud quickly | Minimal Hybrid |
| To avoid making any changes to my network and I want to use the Hybrid Agent as soon as it’s available | Minimal Hybrid |
| To perform a “cutover migration” to Office 365 | Minimal Hybrid |
| To manage Office 365 mailboxes and will be using Azure AD Connect to synchronize my Active Directory | Minimal Hybrid |
| A consistent Global Address List between on-premises and Office 365 | Minimal Hybrid |
| To transfer my organization configuration, like ActiveSync policies to Office 365 | Minimal Hybrid |
| To automatically redirect Outlook clients to Office 365 seamlessly once they migrate | Minimal Hybrid |
| To pre-sync all mailboxes behind the scenes, have automatic delta syncs occur in the background and complete migrations when my organization is ready | Minimal Hybrid |
| To route all mail in and out of the organization through my existing Exchange infrastructure | Full Hybrid |
| To ensure the email path between users on-premises and users in the cloud is secure | Full Hybrid |
| To maintain internal headers on emails, use features like mail-tips cross-premises, voting messages and out of office auto replies | Full Hybrid |
| To see people’s free/busy irrespective of where their mailbox is, on-premises or in Office 365 | Full Hybrid |
| To configure advanced sharing across Exchange and Office 365 mailboxes like Full Access permissions so I can move mailboxes one by one, without being limited by sharing boundaries | Full Hybrid |
| To use advanced integration, like Skype for Business presence, Teams integration into Exchange 2016 mailboxes or cross-premises eDiscovery | Full Hybrid |
Naturally for every scenario above that Minimal Hybrid can be used – full Hybrid will work well too. Hopefully though, you’ll see that the Minimal Hybrid option is worth considering as a go-to option.
Steve is a Microsoft MVP for Office Servers and Services. He enjoys getting hands-on, solving some of the more complex problems associated with migrating to the cloud or to newer versions of Exchange Server.
Hello Steve,
This is very beautiful article, awesome for newbies to understand Hybrid functionality and its uses.
Thanks! I’m glad you found it useful.
Hi Steve. I am in a middle of doing a Hybrid config. I’ve only found out about the minimal hybrid option just recently. When I run the hybrid configuration wizard, minimal hybrid is greyed out and only full hybrid option is available. Maybe it was because of running Azure AD connect previously. How do I undo the full hybrid setup? I have not migrated any mailbox yet. AD users have been synched to office 365 portal. I will be migrating aroung 50 mailboxes only.
Hi, very interested in this answer as well!
Has Hybrid been enabled in the past? Azure AD Connect should not affect whether the option is shown.
Hey Steve,
What if an organization were to change from running a Minimal to FULL ? What would the impact be in doing that change? minimal?
Thanks,
It could be significant, if you are currently using custom connectors for mail flow – these will be created by the wizard.
Microsoft does not recommend minimal hybrid if you are managing your users in your on premises AD infrastructure. Your post seems to disagree with that. Not calling you out, I am curious about your reasoning.
We are starting our 365 migration soon, so I’m needing to make some decisions on how to proceed. I do expect to keep a small on prem Exchange VM for GUI management of Exchange attributes at first, though we may remove that later and go full powershell.
Minimal Hybrid still requires Azure AD Connect to be in place.
Steve
We are trying to make the decision on whether or not to use Full Exchange Hybrid mode for an extended period of time (months or even years). While articles like this one would make one think that this is possible, we have heard war stories that say the opposite. Has anyone successfully ran Full Exchange Hybrid mode for an extended length of time? And, if so, would they be open to answering some basic questions as to lessons learned?
Yes, many have.
Obviously, you are signing up to ensuring your Hybrid environment stays patched and current – so you have to be as regular or better at Exchange patching than your are in the all on-premises world.
Long term Hybrid of course, can mean two different things:
– Running full Exchange Hybrid even though mailboxes have been moved, for Transport/Mail integration and running Autodiscover services
In that case, “Full Hybrid” once all mailboxes have departed, may become, gradually minimal Hybrid as you move DNS records for Autodiscover to Office 365, $null the SCP, and remove Federated Sharing (or unpublish it).
Effectively, it becomes minimal Hybrid with SMTP.
– Running full Exchange Hybrid because you have a balance of Mailboxes that will always remain on-premises, and/or Public Folders
In this case, then you will more than likely need more than “Full Hybrid” as defined by what the HCW creates, as you will be considering Public Folder co-existence , OAuth configuration potentially for Teams (and other) integration with on-premises Exchange, object changes/updates for better levels of Calendar Sharing, Hybrid Modern Authentication – and supporting clients where there are connections to both Office 365 and on-premises in day to day running.
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Versus an on-premises only or a cloud-only deployment this leads back to the patching, and overall service management. Instead of managing Exchange like you did on-premises, you’ve moved to a mostly evergreen model and need to assess new features as they arrive and integrate them. This typically in organisations that run long-term Hybrid goes hand-in-hand with a transition to a new operating model; which of course is key and the most complex aspect to achieve.
Steve