I have previously serenaded about why I consider email a critical service. And for anything you consider critical, you should have a backup of/for it. I use Fastmail as my email host, and this is my weekly workflow for backing it up:
- Fetch all the new emails over IMAP
- Compress the local mail store to
.ziparchive - Store that archive file on my NAS
Fetch emails from Fastmail to a local store
I use the program Mailsync to download from Fastmail using the IMAP protocol. Here's my config and the command I use to run that backup:
mbsync --all --config /Users/varunb/.config/mailsync.rcIMAPAccount fastmail
Host imap.fastmail.com
User contact@example.com
PassCmd "cat /Users/varunb/.secret/FASTMAIL_PASSWORD"
AuthMechs LOGIN
SSLType IMAPS
PipelineDepth 50
IMAPStore fastmail-remote
Account fastmail
MaildirStore fastmail-local
Path /Users/varunb/temp/fastmail/
Inbox /Users/varunb/temp/fastmail/Inbox
SubFolders Verbatim
Channel fastmail
Far :fastmail-remote:
Near :fastmail-local:
Patterns *
Create Near
Expunge Near
SyncState *
Sync PullHere, in line 4, you can see that instead of supplying the credentials for Fastmail directly in the config file, I use a separate file to store the password and use the PassCmd option to tell it how it can find the credentials.
Compress the local store to a zip file
Once Mailsync finishes downloading the emails, I take the whole local store and compress it to a single timestamped .zip file with the highest compression ratio (speed does not matter here as much as space savings matters):
zip --recurse-paths --test --quiet -9 "/Users/varunb/temp/fastmail_2025-08-17_02-12-12.zip"Transfer the archive to NAS
I copy the archive to NAS using a simple cp command and if that is successful then we remove the local archive file. But I let the local mail store around as that reduces the amount of network transfer that has to take place the next time I run mbsync.