I downloaded my Gmail data through Google Takeout and got a big .mbox file (about 4GB). Double clicking does nothing. I am on a MacBook with macOS Sonoma. How do I read the emails?

Apple Mail can import MBOX directly.

1. Open Mail.
2. Choose File > Import Mailboxes.
3. Select "Files in mbox format" and click Continue.
4. Select your .mbox file and click Choose.
5. When it finishes, look in the sidebar under "On My Mac" for a folder called Import (or the file name).

Mail may ask for Full Disk Access if you saved the file in a protected folder. Allow it in System Settings > Privacy & Security.

Imported, but the labels from Gmail are all mixed. Everything is in one folder.

Takeout writes one mbox per label, and Gmail messages with several labels appear in more than one file. If you only see one big mbox you exported everything as one. Re-run Takeout and under "All Mail data included" select only the labels you need, and you get a separate .mbox file for each. Import them one by one and each becomes its own folder.

If you just want to search, import the single big file and use Mail's search. It handles 4GB fine, it only takes a while to index.

Mail finished indexing and search works. Thanks both.