Hybrid Migration vs Cutover Migration: Which Exchange Migration Method Is Better?

A few months back, my IT team lead shared an email regarding the end of Microsoft support for Exchange Server 2016 and 2019. We came to know that Microsoft has discontinued technical support, critical security updates, and bug fixes for both these versions. 

We considered several options to safeguard our messaging environment, and then decided cloud migration (Exchange Online) as one of the feasible options to address the challenge. We had a big task since we had more than 2000 mailboxes hosted on the Exchange Server 2016 environment deployed in our Active Directory (AD). 

We had to create a workable migration strategy for the Exchange server mailboxes and select the ideal method from hybrid and cutover migration to suit the environment. Considering the large number of mailbox users and business-critical emails, a wrong move would have cost migration delays and increased downtime. Here is how we assessed both the methods and eventually chose a preferred approach.

Choosing the right migration method matters

Selecting the suitable method for mailbox migration from Exchange Server to Exchange Online significantly affects the success of your project. The approach chosen to migrate 100 mailboxes may not work for the migration of more than 2000 mailboxes, and vice versa. Several factors play their role in this regard, including:

• Volume of the mailbox
• Network bandwidth
• Compliance-related hassles
• User requirements

To single out the feasible method, we listed the key requirements for the migration job, as follows:

• Reduced downtime
• Handling mass migration with ease and precision
• Minimized obstruction for users
• Uninterrupted email communication
• Safe and secure migration process
• Retain the data after the migration 
• Preserve the permissions for migration
• An alternative strategy in case of a failed migration 

These pointers helped us to choose the ideal method between Cutover Migration and Hybrid Migration. 

But why not staged migration? Well! Since staged migration does not support it, it was out of the question from the start. However, it did help organizations move from legacy Exchange environments, such as Exchange Server 2003 and 2007, to Microsoft 365. But in our case, it was of no use.

Deep insight into both the methods

Before moving forward, we tried to learn the nuances of both the hybrid and the cutover migration. The findings of our research were as follows:  

Cutover Migration

The easiest migration mode to implement, cutover migration, involves moving the entire Exchange server data in one go to Microsoft 365, including the mailboxes, calendars, public folders, and other items. It is suitable for SMEs that wish to quickly and efficiently migrate to a new Exchange server. Here are some crucial aspects associated with it.

• Allows moving the entire email organization to Microsoft 365 in a few days
• Can migrate up to 2000 mailboxes to Office 365 or Microsoft 365, but moving 150 mailboxes at a time is ideal.
• The primary domain name in the Office 365 organization must be the same as that used on the on-premises Exchange environment  
• Users on both the on-premises Exchange mailbox and Microsoft 365 will be the same, but the users will need licenses to access the migrated mailboxes.

Advantages of cutover migration

• Straightforward method
• Does not require maintaining two different but coexisting systems for migration
• The transition takes a minimum time to complete, maybe within a week or a few days
• Prompt access to the new system for all users simultaneously
• Freedom from directory or password synchronizations, or thinking about ways to route internal mail across two live platforms
• Migrates all mailboxes and their items to Microsoft 365 in a single go, making it suitable for small to medium organizations
• Does not need the organization to operate both the old and new systems simultaneously for long time 

Disadvantages of cutover migration

While this method offers multiple advantages, it also has several limitations:

• Since migration happens at once, an unexpected error can cause a high risk of operational disruptions, causing increased downtime.
• An intermittent failure of the operation will require restoring the mailbox to the original system from backups, which can be a time-consuming and complex process.
• Designed specifically for small-scale operations, with organizations often capping batches at 150 users to avoid bottlenecks
• At times, administrators have to perform manual reconfiguration of individual user profiles, desktop settings, etc.
• The old and new systems do not work in parallel, leading the users to be familiar with the new environment immediately

Hybrid Migration

Unlike the cutover method, the hybrid mode allows moving more than 2000 mailbox users to Office 365 in batches, making it an ideal method for use by big corporate houses. In a hybrid migration, there is a seamless and long-term connection between on-premises Exchange Server and Microsoft 365. The connection facilitates the coexistence of mailboxes in both environments, causing slow-paced migration. During the process, it maintains complete functionality on ends, such as shared calendars, a unified global address, and more.

Advantages of hybrid migration

• Allows administrators to move workloads at their own pace instead of migrating entire data at once, while reducing downtime
• Background synchronization of old and new environments enables users to witness a transparent transition. 
• There is no need to reconfigure profiles, as the user credentials, autocomplete data, and calendar permissions remain the same in the new environment
• Allows keeping confidential or sensitive data under on-premises control while moving generic data to the cloud, to maintain regulatory compliance
• Resource sharing can take place seamlessly and at once, across the legacy and cloud systems, making it appear as a single virtual environment.
• Activities like hosting applications on cloud servers, using cloud’s elasticity, or offloading heavy and instant traffic spikes become easier.

Disadvantages of hybrid migration

• Taking care of two separate architectures needs high-end knowledge and expertise
  
  
• The IT teams must have credible experience in monitoring, configuring, and synchronizing the local environment with cloud components
• Organizations have to manage both the physical hardware and the cloud, which requires additional expenses
• Obligations like licensing, networking equipment, and administrative tasks will also increase transition overheads

• Two new environments will increase the responsibility to secure the systems
  
  
• The associated connections, growing vulnerabilities, and the data pipelines between the two environments may give rise to new  vulnerabilities
• Data exchange between the local machine and the cloud can cause performance delays, requiring additional investment in high-speed network connections 
• Synchronization delays may also affect user identities, create data conflicts, and lead to outdated user permissions

The final call

Considering all the aspects of both methods, including the pros and cons, we finally decided to go with the hybrid method. Opting for a cutover migration would have required us to move all the 2000 plus users within a narrow migration window, giving rise to operational risk. Considering our requirements and the high volume of mailbox users, hybrid migration suited us the best.

If you have fewer than 2000 mailboxes or cutover migration suits your requirements, you can always prefer it to the hybrid counterpart. Our technical experts proceeded with the hybrid migration by carrying out the requisite steps. Here is a brief description of the involved steps:

• Exchange Server environment, including the version, AD health, DNS records, and more
• Prepare the Microsoft 365 tenant and verify domain ownership
• Microsoft Entra Connect installation and configuration
• Establish secure connectivity by running the Hybrid Configuration Wizard (HCW)
• Verify the HCW for directory synchronization, Autodiscover, and mail flow functioning
• Configure the migration endpoint in Exchange Online to communicate with the on-premises Exchange server through Mailbox Replication Service (MRS).
• Segregate users into migration batches instead of moving each mailbox simultaneously
• Start batch migration while ensuring coexistence between cloud users and on-premises server
• Proceed with migration validation to verify mailbox access, connectivity, and other aspects
• Complete migration batches to make them functional in Exchange Online
• Update MX, Autodiscover, and DNS records after the migration of all user completes
• Decommission or retain the on-premises Exchange infrastructure as per your needs

These steps helped us to carry out the migration with success. However, due to the manual steps involved, it does include several limitations that we had to overcome. For instance, 

• Need for deep technical knowledge to perform the task 
• Scope for error during the manual method
• The possibility of increased downtime if the process halts somehow

To overcome such hassles, our manager suggested an automated Hybrid Exchange migration the next time we encounter such a requirement. After researching the market, we found Stellar Migrator for Exchange as a suitable option in this regard.

Conclusion

As Microsoft ended technical support for Exchange Server 2016, we had to find a way to secure our mailboxes and the data they contain. After a thorough discussion, we decided to perform the migration of on-premises Exchange to Microsoft 365 (Exchange Online).

We had to choose between cutover and hybrid migration. We analysed both the methods, including their pros and cons. After a thorough study, we chose hybrid migration as we had to move more than 2000 mailbox users. Here, we would like to state that both methods have their respective significance. 

In case you have fewer than 2000 mailboxes, you can choose cutover as well. On second thought, if you find these manual methods cumbersome, you can opt for a hybrid Exchange migration. An automated Exchange migrator, such as Stellar Migrator for Exchange, is a feasible product to fulfil this cause.

Rajesh Kumar

I’m Rajesh Kumar, a DevOps, SRE, DevSecOps, Cloud, and Platform Engineering expert passionate about sharing practical knowledge, real-world experiences, and industry best practices. I have worked at Cotocus and regularly write about technology, travel, investing, health, product reviews, and digital marketing through my various platforms.

I publish technical articles at DevOps School, travel stories at Holiday Landmark, stock market insights at Stocks Mantra, health and fitness guidance at My Medic Plus, product reviews at TrueReviewNow, and SEO and digital marketing strategies at Wizbrand.