In the past I've downloaded my emails from a Gmail account using Google Takeout. This gave me a
.mbox archive. Is there a way I can upload this into a another Gmail account?
Not directly. You'll want to use a third-party email client that can import mbox files as well as connect to Gmail via IMAP.
Thunderbird, with the ImportExportTools extension, looks like it would suit.
Once you import the mbox files and connect your Gmail via IMAP, it then should be as simple as dragging-and-dropping between the accounts.
The following GMail backup/restore utility was recently modified to be able to deal with a Google Takeout file to restore messages to an account. It's the best option available I think.
https://github.com/jay0lee/got-your-back/wiki - free Gmail backup/restore utility, currently command-line only
Once I had the mbox file imported into Thunderbird, I turned on the size column to sort by size and delete any attachments that take an email's size over 10 or 15 MB (causes time-out errors). Then I uploaded to my Gmail account in blocks of 10,000 or so emails. I tried some 20,000 and 30,000 blocks with mixed results. The emails upload at about 1 per second, depending on the size of attachments. I was happy to transfer 30,000 emails in a day... just letting it run in the background. Remember to set your laptop's energy setting to not go to sleep...
Imap-Upload does it as well, and no need for thunderbird + extension + manual workflow.
GYB(Got Your Back) can import .mbox files to Gmail.
gyb --email firstname.lastname@example.org --action restore-mbox --local-folder <relative path to folder containing your .mbox file(s)>
Perhaps only available to Business but a Google to Google solution is as follows:
- Go to Manage this Domain/Admin. (Need to be super admin).
- Click on the Migration Button.
- Use the plus icon and then login/verify the old Google Account.
- Add the new account email address.
Submit and Wait for it to 'migrate' all emails.
It is actually the same idea as downloading the archive and then using 3rd party software via IMAP, but instead of archiving and downloading etc. you use IMAP directly between the 2 accounts
To ensure Folder/Label structure is kept, after turning on IMAP access on the old account, you can ensure 'show in IMAP' is checked under Settings->Labels.