A native macOS app to back up and restore IMAP mailboxes as standard .mbox files.
No dependency on Apple Mail, no third-party service.
Direct IMAP/TLS connection on port 993, incremental backups, full local archive in an open format you actually own.
- Direct IMAP backup over TLS (port 993). Works with Gmail, iCloud, Fastmail, Proton Bridge, self-hosted Dovecot/Cyrus, etc.
- Incremental sync based on
UIDVALIDITY+ per-folder UID tracking. Re-runs only download new messages. - Configurable message filter per account: All / Read only / Unread only / Flagged.
- Full archive mode (per account, opt-in): writes one self-contained
.emlper message — a real, standards-compliant email you can re-import into any mail client, with remote hot-linked images fetched and embedded ascid:inline parts and attachments included. Your mail stays complete even after the sender drops the images. - Open archive format: Unix
.mboxfiles split by year-month, plus a sidecar JSON index for fast browsing. Messages are stored byte-for-byte (non-UTF-8 safe). - Built-in viewer: read backed-up emails directly inside the app — remote images are blocked by default for privacy, with per-message opt-in.
- Restore entire folders or individual messages back to any IMAP server, original
INTERNALDATEpreserved. - Import existing
.mboxfiles from Apple Mail / Thunderbird / other backups. - Scheduled backups per account (15 min → 7 days).
- Menu-bar companion with quick backup status.
- Passwords stored in the macOS Keychain, never in plaintext.
- App Sandbox enabled, minimal entitlements (network client + user-selected files only).
- Read-only on the server: backup uses
BODY.PEEK[]and never sets the\Seenflag.
- Download
MailKeep-1.8.6.zipfrom the latest release. - Unzip and move
MailKeep.appinto/Applications. - First launch: right-click → Open to bypass Gatekeeper (the app is signed ad-hoc, not notarised).
- Pick a backup folder when prompted — this is where
.mboxfiles will be written.
Universal binary (Apple Silicon + Intel) · macOS 14 (Sonoma) or later.
Gmail / iCloud note: OAuth2 is not supported yet — these providers require an app-specific password instead of your regular password.
- Add an account — server, username, password. Click Test connection.
- Pick folders to back up (INBOX, Sent, Archives…).
- Choose what to back up — by default only read messages are saved; switch to All if you want everything.
- Hit Back up all (
⌘⇧B) and watch the per-folder progress. - Optional: enable scheduled backups to run every N minutes/hours.
| What | Where |
|---|---|
Mailboxes (.mbox files, one per year-month) |
The folder you picked at first launch |
| Search index (JSON, per folder) | Same folder, next to the .mbox |
Full-archive copies (.eml, one per mail, when enabled) |
archive/ subfolder next to the .mbox |
| UID state (per folder) | ~/Library/Containers/com.mailkeep.MailKeep/Data/Library/Application Support/ |
| IMAP passwords | macOS Keychain (service com.mailkeep.MailKeep.imap) |
The .mbox files use the standard Unix format with From line escaping. You can open them with any mbox-aware tool (Apple Mail Import, Thunderbird, mbox-parser, scripts…).
- Full folder: pick a
.mboxfile and a destination folder on the server.INTERNALDATEis preserved from the originalFromline. - Single message: open it in the viewer and use Restore.
Restored messages arrive flagged \Seen (server-side limitation: original flags are not stored in mbox).
SELECTthe folder, readUIDVALIDITYandUIDNEXT.- If
UIDVALIDITYchanged → wipe local state for that folder. - Run
UID SEARCH <filter>(e.g.SEEN) — server returns the full UID list matching the filter. - Subtract the UIDs already on disk → fetch only the new ones.
- Each message is appended to the right
.mboxfile (<folder>_YYYY-MM.mbox), indexed, and its UID added to local state. - UID state is flushed every 50 messages and the index every 250, so an interrupted run resumes cleanly.
UID FETCH uses BODY.PEEK[], so the \Seen flag is never changed on the server.
The .mbox always contains the complete message, so inline images and attachments are already saved. What is not in any email are remote hot-linked images (<img src="https://…">) — they live on the sender's server and vanish when it drops them.
Enable Full archive on an account (Settings → Archive complète, off by default) to also write a self-contained .eml per message in the archive/ folder:
- A real, standards-compliant email — re-importable into any mail client (Apple Mail, Thunderbird, Outlook…).
- Remote images fetched and embedded as
cid:inline parts (responses are validated as real images, so CDN error pages aren't stored). - Attachments included (RFC 2231 filename encoding for non-ASCII names).
In the app, the email viewer shows the offline copy via the Copie archivée button. The .mbox stays the byte-exact canonical backup; the .eml is a separate portable copy.
Tradeoff: fetching remote images makes HTTP requests to sender servers at backup time, revealing your IP — the same thing the viewer's blocker prevents. That's why it's opt-in.
Already ran a Full-archive backup on 1.7/1.8.0? Those
.emlfiles predate the 1.8.1 fixes — re-run the backup for those folders to regenerate them.
Requirements:
- macOS 14 SDK or newer
- Xcode 15+
- Swift 5.9+
git clone https://github.com/Kitround/MailKeep.git
cd MailKeep
open MailKeep.xcodeprojThen ⌘R to build & run. No external dependencies, no package manager — pure SwiftUI + Foundation + Network framework.
MailKeep/
├── Engine/ Backup orchestrator + scheduler
├── IMAP/ Low-level IMAP client (TLS via NWConnection)
├── Models/ IMAPAccount, AppState, BackupRun, EmailMessage…
├── Storage/ Mbox read/write, JSON index, Keychain, state files
└── Views/ SwiftUI views (sidebar, list, detail, settings…)
MIT — see LICENSE.
Issues and PRs welcome. Please keep changes focused and explain why in the description.