You can bulk migrate multiple Thunderbird accounts to Office 365 by using the SysInfo Thunderbird to Office 365 Converter. The software is designed to transfer large Thunderbird mailboxes directly into Microsoft 365 without manual configuration or data loss.
After installing the tool, it automatically detects Thunderbird mailbox data from your system. You can add and manage multiple Thunderbird accounts or mailbox folders at once, preview the emails, and select the required folders for migration. Then, choose Office 365 as the destination platform and sign in with your Microsoft 365 account credentials.
The tool transfers emails, attachments, calendars, tasks, and other mailbox items in bulk while maintaining the original folder hierarchy and email formatting. It also includes useful features like duplicate email removal, date range filters, and attachment management, which help make large-scale Thunderbird to Office 365 migration more organized and efficient.`1
Migrating multiple Thunderbird accounts to Office 365 is one of those tasks that sounds straightforward on the surface but quickly reveals its complexity once you're in the middle of it. Thunderbird stores email data in MBOX format across individual profile folders for each account — scattered throughout your system with no built-in export feature to package everything neatly for migration. When you multiply that across dozens of accounts, the manual effort becomes completely unmanageable, and the risk of losing emails, dropping attachments, or breaking folder structures grows significantly with every additional mailbox you're trying to move. The core challenge is that Thunderbird and Office 365 operate on fundamentally different architectures, and bridging that gap at scale requires a dedicated tool rather than a manual workaround. The MacSonik Thunderbird Backup tool is purpose-built for exactly this scenario — it automatically detects all your Thunderbird profiles, processes multiple accounts in a single batch operation, and converts all email data into PST format, which Office 365 accepts natively through its standard import workflow. Every email's folder hierarchy, metadata, timestamps, attachments, and original formatting are preserved with complete accuracy throughout the process, eliminating the guesswork and data loss risks that come with manual migration attempts. Once your PST files are ready, you simply use the Office 365 admin center's import feature to bring everything across cleanly. For anyone managing a business or team transition away from Thunderbird, this is the most efficient and reliable path to Office 365 without the usual migration headaches.
If you are looking for an easy solution to bulk migrate multiple Thunderbird accounts to Office 365, this discussion is it. We will show you one of the top professional tools. This program will effortlessly and quickly migrate your Thunderbird data to Outlook 365. WholeClear Thunderbird to Office 365 Converter tool is one of the best tools to convert Thunderbird data to Office 365. It is the most popular program as it contains many advanced features. Plus, you get a free trial pack that converts the first 25 items from the Thunderbird mbox folder to Office 365. This can be used to verify the software.
