Our IT team is reviewing how to handle Microsoft 365 mailbox data during a possible platform change, and I’m trying to understand which parts of the process usually require the most planning. At first, email migration looks straightforward, but once you include archive mailboxes, contacts, calendars, folders, attachments, and large numbers of users, the project becomes considerably more complicated.

For example, organizations that migrate Office 365 to Google Workspace need to plan more than just mailbox transfers. Source and destination accounts must be mapped correctly, authentication needs to be configured, and administrators should verify that important mailbox data reaches the correct users. Running a small test group before starting the complete migration seems like a sensible way to identify problems early.

Another consideration is data selection. Some businesses may want to transfer their complete mailbox history, while others may only need specific folders or emails from a defined period. Date-based filtering can reduce the amount of unnecessary information being processed. Duplicate handling is also important because repeated messages can make destination mailboxes harder to manage.

At the same time, I think organizations should maintain an independent backup strategy. Even if the migration completes successfully, having an additional copy of important Microsoft 365 data can be useful for recovery and compliance purposes. This is where Office 365 Backup Software can be helpful, particularly when administrators need to back up primary mailboxes, archive mailboxes, and public folders before making major changes to the environment.

Another feature worth considering is incremental processing. If users continue working while the initial backup or migration is underway, new emails may arrive after the first operation. Reprocessing every mailbox from the beginning is inefficient, so being able to skip previously processed items and capture only new data can simplify the final stage.

During my research, I found the DRS Softech Office 365 Backup Tool, which lists support for mailbox preview, Modern Authentication, Client ID authentication, CSV-based bulk processing, advanced date filtering, duplicate removal, incremental backup, custom folder naming, PST splitting, and export to several formats. It also provides options for backing up data to other cloud environments.

I’d like to hear from people who have already managed a large Microsoft 365 backup or migration. What did you consider essential before starting? Did you create a full backup first, test a few accounts, or divide users into multiple migration batches? Also, how did you verify the final mailbox data once the project was completed?