How do I export a mailbox larger than 50 GB from Microsoft 365?

[raj.aryson24]

Exporting a Microsoft 365 mailbox larger than 50 GB can become difficult when users need to move large amounts of emails, attachments, and folders without losing important mailbox data. Large mailboxes often contain years of communication records, making manual export methods slower and more complicated. Outlook’s built-in export process depends on mailbox synchronization and may become challenging when handling oversized mailboxes, resulting in long processing times, incomplete exports, or difficulties managing large PST files. Microsoft 365 administrators and users need a reliable way to export large mailbox data while maintaining the original email structure and folder organization.

A dedicated backup solution can make the process easier by allowing users to create local copies of Microsoft 365 mailbox data without depending completely on manual export methods. The SysInfo Office 365 Backup Tool helps users export large Office 365 mailboxes into PST and other formats while preserving emails, attachments, and folder hierarchy. It supports selective mailbox backup, allowing users to export required folders instead of processing unnecessary data. Features like date range filtering help export emails from a specific period, while duplicate removal prevents repeated email items during backup. The tool also provides PST splitting functionality to divide large PST files into smaller manageable parts for easier access in Microsoft Outlook.

The software supports exporting Microsoft 365 mailbox data into formats such as PST, EML, MSG, MBOX, and PDF according to user requirements. It maintains email properties and attachments throughout the backup process, helping users keep their data organized and accessible. With support for handling large mailbox exports, the SysInfo Office 365 Backup Tool provides an efficient way for IT administrators and organizations to back up Microsoft 365 mailboxes exceeding 50 GB for migration, archiving, compliance, or recovery purposes.

[Zenifer]

If you're dealing with a Microsoft 365 mailbox that's larger than 50 GB, this is actually a fairly common challenge. I had a similar situation while helping migrate a user's mailbox, and one thing I learned is that exporting everything into a single PST isn't always the best approach. Even though Outlook supports large Unicode PST files, extremely large PSTs can become difficult to manage, take longer to open, slow down searches, and increase the risk of corruption if something goes wrong during or after the export.

The first thing I would suggest is checking whether you can export the mailbox in smaller chunks. For example, exporting emails by date range (such as one year at a time) or by specific folders can make the process much smoother. It also makes future backups and restores much easier because you're working with smaller, organized PST files instead of one massive archive.

If you've already exported the mailbox into a single large PST, you don't necessarily have to repeat the export. In that case, splitting the PST afterward is often the easier solution. I had good results using Stellar Splitter for Outlook for this purpose. It allows you to split a large PST by size, date, year, or folder while preserving the original folder hierarchy and email structure. That saved me from manually creating multiple PST files and moving thousands of emails around, which would have taken a lot of time.

Another advantage of having multiple smaller PST files is that Outlook performs noticeably better. Opening the mailbox is quicker, searches are faster, and it's easier to archive or share specific portions of the mailbox when needed. If you're keeping the exported data for compliance or long-term storage, having separate PST files by year or department also makes finding older emails much simpler.

Before starting any export or split operation, I'd strongly recommend creating a backup of the mailbox or the original PST file. It's a simple precaution, but it can save a lot of trouble if the process gets interrupted or if you need to restore the original data.

So, if your mailbox is over 50 GB, I'd avoid relying on a single oversized PST whenever possible. Either export the mailbox into smaller sections from the beginning or, if you already have one large PST, use a reliable PST splitting tool like Stellar Splitter for Outlook to divide it into manageable files. In my experience, it's a much cleaner and safer way to handle large Microsoft 365 mailbox exports.