Backup e-mail (revisited)

I recently blogged about my e-mail backup strategy, using imap-backup. However I’ve found in real life this tool trips up quite a lot, and doesn’t really sync very satisfactorily on an ongoing basis.

It’s also been slightly nagging at me that I’m just mirroring – so if an e-mail is deleted it’s gone for good once the next backup has run. But equally I didn’t want to have to backup the whole shebang every time.

So, the solution I’ve reached is a combination of offlineimap and my old friend restic to do incremental backups securely and efficiently. The restic repository also goes up to good old sync.com, which is potentially a bit of duplication – but I wanted the snapshot capability (rather than individual file histories).

Basic workflow is

1. Use offlineimap to mirror the imap server into local maildir folders
2. Use restic to take a snapshot of the maildir folders

Of course, this is all done using Docker containers. So step one uses a volume within the docker container, step 2 uses a local filesystem mount for the restic repository.

Dockerfile

Pretty standard – install offlineimap and restic, then copy across the config file to ~/.offlineimaprc. Worth saying that ~/.offlineimaprc has passwords in it, so this image shouldn’t be published anywhere!

.offlineimaprc

Best off reading the docs, but this is what I had to do to get it working nicely. Looking at it again now, the windows stuff and nametrans may no longer be required, as I originally used a mounted windows volume rather than a native docker volume for this step.

Of course you can add as many accounts as you want.

Backup.bat

This is slightly more involved. I’ve got the best outcome when I sync each account individually. This script spins up a docker container for each account in turn, with a named volume mount called offlineimap which stores the local maildir (so it persists between runs). Then it spins up a final docker container to do the restic business.

That last line is a bit more involved it has to mount two volumes – the offlineimap as above, but then a Windows folder on my host PC mounted at /restic which stores the restic repository. This Windows folder is one managed by sync.com. As you can see, I needed to add some extra bits and pieces to the restic command to get it to do the incremental backup properly with a mounted windows volume.

In action

The first run is slow, as it has to download entire mailboxes, but thereafter it’s only a few seconds per account.

The abridged log output is shown below. The numbers won’t add up as this is from one of my actual runs, which syncs 6 or 7 e-mail accounts.