Best Practices for Migrating Large Mailboxes

https://www.infosecurity-magazine.com/blogs/migrating-large-mailboxes-from/

Publish Date: 2026-06-18 10:17:44

Source Domain: www.infosecurity-magazine.com

Migrating Large Mailboxes to Microsoft 365

Migrating large mailboxes, particularly those exceeding 100GB, presents unique challenges that raise the risk of issues like timeouts, throttling, and data corruption. This article lays out the best practices for migrating oversized mailboxes from local Exchange Server to Microsoft 365. Several reasons cause migration failures, including throttling policies from Microsoft 365, connection timeouts due to bandwidth and server performance limitations, size restrictions of Microsoft 365 plans, and corrupted mailbox items.

To migrate large mailboxes efficiently, there are two recommended approaches. First, utilize native Exchange tools with optimization. This involves enabling an online archive mailbox by provisioning an Enterprise E3 license, incrementally migrating the mailboxes, increasing the move request size limit, and scheduling migrations during off-peak hours to mitigate throttling effects. Second, consider using a third-party migration tool like Stellar Migrator for Exchange, which operates independently of the Exchange Server infrastructure, automates processes, provides incremental migration support, enhances reporting, and maintains data integrity.

Key Points:

Migrating large mailboxes of over 100GB has risks such as throttling and data timeouts.
Several reasons cause migration failures, including throttling, data timeouts, size limitations, and corrupted mailbox items.
There are two recommended approaches: using native Exchange tools and third-party migration tools.
Native migration benefits include incremental data migration, auto-expanding archive, and off-peak migration scheduling.
Stellar Migrator for Exchange offers advantages like eliminating the need to manually split data and supporting incremental migration methods.