Selfhosted

"GMail takeout files" aren't a thing. mbox is a standard file format from Unix. Some Unix-likes provide the mail command and on others you have to install s-nail, after which you can do mail -f {path to mbox} to view all mail inside. If there are multiple files, you can literally just concatenate them like so: cat /somedirectory/*.mbox > theultimate.mbox.

Apart from that, most GUI mail clients allow viewing mbox. When the mbox file updates, the client says you have new mail. For example, in Claws Mail, skip setup, then go to plugins and enable the mbox plugin (while you are there, may as well enable pgp, s/mime, calendar, dillo to handle all formats). Then, go to create new account, and in the "Basics" tab, select "local mbox file" for "Receive protocol ". It will then ask for a file path.

Also, if your Google account settings allow, you can literally just login to Google from Claws mail. Set protocol to IMAP, then set Authentication method to Oauth2 in both Receive and Send tabs. Proceed with setup as usual and it will open your default web browser to login. After that, it will download your entire history of mail.

What worked for me was I installed and ran Thunderbird, then I quit and copied the Google Takeout .mbox file to ~/.thunderbird/xxxxxx.default-esr/Mail/Local Folders. When I re-launched Thunderbird, it took a few minutes and then all my Google Takeout emails were browsable/searchable under Local Folders.

Also, I think there was a weird step involved, like I needed Thunderbird to connect to some email account, any email account, in order to get past the welcome screen.

I use this to archive multiple email accounts

https://github.com/rustmailer/bichon

You could just install dovecot and search over imap or pop3 from any email client.

I don’t really use any e-mail clients on my computer

Curious as to why. Is it a security issue or is it just not convenient.....

Thunderbird will import .mbox files but you'll need a plugin called ImportExportTools NG.

Import:

• Mbox files (including structure)
• EML & EMLX files
• Individual or all directory files

A friend uses: https://github.com/LogicLabs-OU/OpenArchiver

Also I have been meaning to release the one I've been working on so I won't mention more about that.

• You can use imapsync to sync all you mails from GMail to your new email provider if you still use email.
• If you no longer use email, Piler is a bit heavy but well-working solution.
• Notmuch is much lightweight but has no web UI, but if it require you install a (may be TUI) software, why not just install a mail client like Thunderbird and then just use its local mail feature to index the mbox?

I’d just add both Gmail and another email account to a desktop email client, then simply drag the emails from one provider to the other.

Alternative approach: I imported the mails to my new mail hoster and just archived the mbox files just in case. Can be done by installing a mail client temporarily to upload or some mail hosters provide an option to import from gmail (in my case that was proton)

My suggestion would be to stand up a mail server (that doesn't really do anything) and bring your mail over there. Then add the account on your phone, and you've got email now searchable like any other.

there's few old scripts (mostly for mailing list archive usage) that takes mbox input and outputs html. not pretty but they could work in this case. searching is another issue though

it's not FOSS (it is 'free to use' at home) or a 'server' application (it's a windows application), but i just use mailstore home to create and update a local archive of a gmail account. its dot.net requirement is minimal (v4.8 or higher) but i have not yet tried to run it with wine, as i have a separate box that runs windows stuff.

https://www.mailstore.com/de/produkte/mailstore-home/
https://www.mailstore.com/en/products/mailstore-home/