Migrating large mailboxes from Zimbra to Office 365 can be a complex and time-consuming process. To ensure a smooth migration, it's essential to implement effective strategies for managing these mailboxes.

Mailbox Archiving: Consider archiving old emails to reduce mailbox sizes before migration. This can significantly speed up the migration process and improve performance.

Incremental Migration: Instead of migrating entire mailboxes at once, consider migrating data in batches or increments. This approach can help manage network traffic and reduce the risk of errors.

Migration Tool Selection: Choose a migration tool that is specifically designed to handle large mailboxes efficiently. Look for tools that support incremental migration, parallel processing, and progress tracking.

Network Optimization: Ensure sufficient bandwidth and network stability during the migration process. Prioritize migration traffic and address any network bottlenecks.

Mailbox Capping: Implement mailbox size limits to prevent the creation of excessively large mailboxes in the future. This can be done through policies and user education.

By following these strategies, organizations can effectively manage large mailboxes during the Zimbra to Office 365 migration process, minimizing disruptions and ensuring a successful transition.