Export an Outlook PST file to EML using Thunderbird

Zero budget project: I need a 4GB PST turned into EML files and I keep reading Thunderbird can do it for free.

Thunderbird does not open PST files though. What is the actual procedure people use?

Correct, Thunderbird never touches the PST itself. The free method relays the mail through an IMAP server that both clients connect to. Outlook uploads, Thunderbird downloads, then a Thunderbird add-on writes EML.

1

Create or reuse an IMAP mailbox with enough quota, a free Gmail account gives 15GB which covers your 4GB.

2

Add that account in Outlook, open the PST alongside it and drag folders from the PST into the IMAP account. Let each folder finish syncing before the next, the status bar shows progress.

3

Install Thunderbird, add the same IMAP account and let it download everything. In account settings enable offline storage for all folders so full copies land locally.

4

Install the ImportExportTools NG add-on. Right click each folder, ImportExportTools NG, Export all messages in the folder, EML format, and pick your output directory.

Honest expectations for 4GB: the double transfer through IMAP takes several hours to a day on office bandwidth and Gmail throttles sustained uploads, so start it before a weekend. Calendar and contacts do not travel over IMAP at all. If the timeline is tight, a direct PST to EML converter does the same job locally in under an hour, which is the trade against the zero cost.

Started the upload Friday evening, exported EML on Sunday. Slow like you warned but the price was right. 31,000 files out clean.