I知 dealing with a Microsoft 365 mailbox where the Online Archive has grown to roughly 370 GB. The requirement is to create PST backups separated by year, but the export I started through Outlook has been running for several days without an obvious change in the archive size. I知 trying to understand whether this is simply a matter of waiting or whether there is a better way to approach such a large export.

The Online Archive is visible in Outlook, so I initially used the Import/Export option and selected the archive mailbox. This works for smaller exports, but I知 concerned about using the same approach for hundreds of gigabytes. A long-running process can be difficult to monitor, and if something goes wrong near the end, repeating the export would be a major inconvenience.

One thing I知 considering is Export Online Archive to PST using smaller date-based selections. Since the requirement is to separate the data by year anyway, exporting one period at a time seems easier to manage than creating one enormous PST. It should also make the resulting files easier to verify and store.

I also looked at Microsoft 365 eDiscovery. It provides another way to collect mailbox information, particularly when the data is needed for legal or compliance purposes. However, configuring the required permissions, search, collection, review, and export steps adds another layer of administration.

For a large archive, I came across the SysInfo Microsoft 365 to PST Export Tool as another approach. The information I found says it can export Exchange Online Archive mailboxes without Outlook and supports date filters, duplicate removal, skipping previously exported items, and splitting large PST files. It also supports Exchange Online, on-premises Exchange, and hybrid environments.

The filtering options are probably the most relevant feature for my situation. Rather than processing the complete archive repeatedly, I could select a particular year, export it, verify the resulting PST, and then move on to the next period.

Has anyone dealt with an archive around this size? I知 particularly interested in whether Office 365 archive mailbox to PST exports are easier to manage when divided by year, and what method you used to verify folders, emails, attachments, and older archived messages afterward.