How can I migrate all mailboxes

Hi @Montez Martha

Thank you for posting your question in Microsoft Q&A. 

We understand that you are considering migrating mailboxes from Exchange Server 2013 to Exchange Server 2019. 

Based on my research, you could consider migration path from Exchange 2013 > Exchange 2016 > Exchange 2019. Exchange 2019 supports coexistence with Exchange 2016, better than Exchange 2013. Exchange 2016 acts as a bridge because it understands both the older protocols used by Exchange 2013 and the newer architecture of Exchange 2019, ensuring client connectivity and service continuity during migration. 

Note: Exchange does not support in-place upgrades between major versions (from Exchange 2013 directly to 2016 or 2019). A new server must be deployed for each version, and mailboxes/services migrated accordingly.

Following the native upgrade path is important for several reasons: 

It ensures proper coexistence and client access because Exchange 2016 can handle namespace and virtual directory alignment, allowing Autodiscover, Outlook Web Access, and other services to work seamlessly during the transition.  

Public folder migration requires Exchange 2016 as an intermediary since Exchange 2013 public folders cannot be moved directly to Exchange 2019.  

If you plan to implement or maintain a hybrid environment with Exchange Online, Exchange 2016 is the recommended hybrid server, making future flexibility easier.  

Finally, using the native path reduces security and compatibility risks 

In my opinion, the best practice is to follow the supported migration path: upgrade Exchange 2013 to the latest CU, deploy Exchange 2016, migrate mailboxes and services to Exchange 2016, then introduce Exchange 2019 and complete the migration. This approach is secure, supported, and minimizes risk, ensuring a smooth transition for users and administrators. 

Regarding your friend’s suggested approach, this is unnecessary for an on-premises migration. You do not need to route through Exchange 2016, then sync to Exchange Online, and then back to Exchange 2019. That sounds like an overly complex hybrid migration path, which is typically used only if you plan to temporarily move to the cloud and later return to on-premises. 

For migrate plan directly from 2013 to 2019, this approach may require introducing an Exchange 2019 server into the existing Active Directory forest for coexistence, followed by performing batch mailbox migrations. However, coexistence with Exchange 2013 is no longer supported in the latest builds, installation will fail if any Exchange 2013 servers are detected in the organization. To make this work, you may need to obtain and install an older cumulative update (CU) for Exchange 2019 (for example, CU14 or earlier, if available through Microsoft support or archives) that still allows coexistence. After completing the migration and decommissioning all Exchange 2013 servers, you can then update Exchange 2019 to CU15 or later.  

But it might risky:  

Security vulnerabilities: Older CUs lack critical patches.  

Compatibility issues: Upgrading later may break namespaces, certificates, or public folder configuration.  

High operational risk: Not a best practice for production environments.  

You can refer more via: 

Exchange 2013 servers can't coexist with Exchange Server 2019 CU15 [E19E15CoexistenceRequirement] |… 

Exchange Deployment Assistant | Migrate mailboxes to Microsoft 365 

Mailbox moves in Exchange Server | Microsoft Learn 

Exchange Server build numbers and release dates | Microsoft Learn 

Best Practices for Migrating from Exchange Server 2013 to Exchange Server 2019 | Microsoft Communit… 

Please note that this summary reflects my own findings and may not fully represent the most suitable approach for your concern. To help you reach your goal more effectively, I recommend posting a thread on the Microsoft Tech Community forum. It’s a great platform for deeper technical discussions and connecting with individuals who have hands-on experience and expertise. They’re best positioned to provide guidance and valuable insights on this topic. 

If you have any additional concerns, feel free to comment below. I would be more than happy to assist. 

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".      

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.