gbackup-rs VS offlineimap3

https://github.com/djipko/gbackup-rs

Produces an SQLite database.

I suspect your new mail server supports IMAP. So you can run offlineimap to "sync" mails from Proton Mail to your server, as long as you have Proton Mail Bridge available.

I have also configured it that no deletes are synced, so I don't loose anything I delete by accident (sync_deletes). Also set the folderfilter to your liking. For all options check out https://github.com/OfflineIMAP/offlineimap3/blob/master/offlineimap.conf

Offlineimap can backup Gmail without problems, including the labels (they are added as X-Keywords header to the mail).

You can synchronize your email off gmail using offlineimap or any other similar program (you can and also should make a full request of your data with Google right now, because even an unmanaged dump can serve as a backup copy). You could then ensure you lose nothing by version-controlling the resulting maildir using git.

Part of this is due to bad software design. The email server provides a service, but nothing prevents you from backing up the emails you synchronize... except for software that doesn't allow it because the devs didn't give a shit.

So I have to ask, why JMAP? And does anything like offlineJMAP exist?

i can not longer use mu4e with my outlook account because of 2FA. I used to set it up through a combo of DavMail and offlineimap3, but now that doesn't work because DavMail can no longer create a bridge between outlook and imap, since I don' know how to get it working with 2FA.

On https://www.offlineimap.org there is still a link to the repository that uses Python 2 which is no longer supported. At https://github.com/OfflineIMAP/offlineimap3, development apparently continues with Python 3. There is version 8.0.0 available (https://github.com/OfflineIMAP/offlineimap3/releases/tag/v8.0.0)