📬 isync

isync, the project behind the mbsync command, in a small rootless image: two-way synchronization between two IMAP servers, or an IMAP server and a local Maildir. It keeps state between runs, so moves, flags and deletions on either side reach the other.

Usage

The image runs mbsync (Alpine, isync 1.5.1) as UID 65532 and accepts any UID in group 0, with a read-only root filesystem. Mount a config and a writable state directory, and let the platform schedule it (a Kubernetes CronJob or a systemd timer); nothing in the image runs on a timer. Arguments starting with - go to mbsync; any other command (sh, a script) runs as given.

docker run --rm --read-only \
  -v ./mbsyncrc:/etc/mbsyncrc:ro \
  -v ./secrets:/run/secrets:ro \
  -v mbsync-state:/var/lib/mbsync \
  hlhd/isync -c /etc/mbsyncrc -a

• /var/lib/mbsync: sync state. Keep it between runs; without it the next run cannot tell a deletion from a new message.
• Passwords come from files at run time, never from the config: PassCmd "cat /run/secrets/<name>".
• TLS 1.2 and 1.3 only, certificates verified.

Two-way sync between two IMAP servers, here a Gmail account and a self-hosted mailbox:

IMAPAccount gmail
Host imap.gmail.com
User someone@gmail.com
PassCmd "cat /run/secrets/gmail"
TLSType IMAPS
TLSVersions +1.2 +1.3

IMAPAccount home
Host imap.example.com
User someone@example.com
PassCmd "cat /run/secrets/home"
TLSType IMAPS
TLSVersions +1.2 +1.3

IMAPStore gmail
Account gmail

IMAPStore home
Account home

Channel mail
Far :gmail:
Near :home:
# Gmail shows every message under "All Mail" and again under each label;
# syncing it would duplicate everything.
Patterns * !"[Gmail]/All Mail" !"[Gmail]/Important" !"[Gmail]/Starred"
Create Both
Remove Both
Expunge Both
Sync All
CopyArrivalDate yes
SyncState /var/lib/mbsync/

License

isync is GPL-2.0-or-later; this packaging follows it.