Choosing between Minimal and Full Exchange Hybrid

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:

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 Goodman

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.