Comment by sneak

A good workaround for email hosting is to run an IMAP server somewhere you control, and add it to your mail client. The server doesn’t need 24/7 five-nines or anything. It’s not for receiving mail. It could even be on your local laptop if that is the only place you need old mail, though I keep mine on a dedicated hosting machine in a colo so I can use/search it from my iPhones and iPads and other workstations.

You use an IMAP compatible email service like Proton or whatever to receive and check mail like normal. A couple times per month, move all the messages from the service to your own IMAP server’s folders, instead of the “archive” command that moves them to a different folder on the same server that received them. This is pretty straightforward in Apple’s Mail.app on macOS, and I imagine similarly so in most GUI IMAP clients.

This gives you the best of both worlds: a single set of maildir folders on your own server you can zip or back up with normal tools like rsync or whatever, as well as 24/7 HA reliable provider servers to receive incoming mail at all times in case your long term mail storage machine is temporarily down. You also won’t bump up against provider storage limits.

Self-hosting inbound and outbound email is a drag (though I do it for many of my less critical domains), but a 90% availability selfhosted message storage IMAP service is fairly easy to run. This has the added benefit of a provider hack or legal process presumably affecting only a subset of your most recent messages due to those being the only ones stored there.

I am a Proton and FastMail user (and use the affected software) but I regularly move all the messages from these providers to my IMAP storage server (in different folders) so if their systems fail the blast radius is not “all of my emails going back to whenever I started using the provider”.