Google doesn’t offer a direct way to import an MBOX file back into Gmail, which can be frustrating. However, you can use Thunderbird (a free email client) to manually upload the emails:
1. Add your new Gmail account to Thunderbird using IMAP.
2. Install the ImportExportTools NG add-on.
3. Use it to import your MBOX file into Thunderbird.
4. Drag and drop the imported emails into your new Gmail inbox.
If this sounds too complex or time-consuming, you can use a third-party tool like
Advik MBOX to Gmail Import Tool, which allows you to upload MBOX files directly into your new Gmail account without needing Thunderbird. It’s an easy, automated way to transfer all your emails safely.