stalwart-migrator

In-place upgrade tool for Stalwart Mail Server, 0.15.5 → latest: no data loss, a checkpoint at every step so an interrupted run resumes instead of restarting, and automated validation that the server still works afterwards.

Recovery from a failed migration is your own snapshot or backup — this tool does not undo a migration. See Recovery is your job before using it on anything you care about.

Go, standard library only — no external dependencies.

This has been used to migrate a production mail server. On 2026-08-25 it took a live server — nine domains, six accounts, a 2.4 GB RocksDB store — from 0.15.5 to 0.16.19 with 8 seconds of downtime, every phase green including post-cutover validation, mail flowing before and after. That run was preceded by a full dress rehearsal on a clone of the same server, which is the practice this project most recommends copying: see Rehearse on a clone first.

Before you start: two things you must fix on the server

Neither is something this tool can do for you, and both stop a migration dead. preflight refuses on both, while the mail server is still running — but they are worth knowing before you book a maintenance window, because fixing them is a change to your directory, not a flag.

1. Remove or collapse multi-tenancy. v0.16 requires a tenant-scoped account to sit on a domain owned by that same tenant, for its primary domain and every alias. v0.15 imposed no such rule, so an install that is perfectly valid today can be unrepresentable in v0.16. Run stalwart-migrate tenants to see who owns what. Where a domain has no tenant of its own and only one tenant's accounts use it, the conversion repairs it for you; where two tenants genuinely share a domain, nothing can, and you must resolve it in v0.15 first — give each tenant its own domains, move the accounts into one tenant, or remove the tenants entirely.

2. Migrate as a directory account, not the built-in admin. A [authentication.fallback-admin] from config.toml authenticates perfectly well right up to the moment the migration finishes, and then stops existing — v0.16 keeps its configuration in the store, so the block defining it is never read again. The migration itself still succeeds; what you lose is the ability to verify it, recalculate quotas, or administer the server afterwards. See You need a named admin account.

Status

Roughly 14,600 lines of Go, stdlib only, of which about 6,300 are tests. Every phase exists as a package and run wires them into the migration described above.

Command	State
stalwart-migrate preflight	Works — read-only checks and a migration plan
stalwart-migrate rehearse	Works — read-only; converts your settings and reports what won't carry over
stalwart-migrate run	Works — performs the migration; --recovery-point-confirmed --yes
stalwart-migrate tenants	Works — read-only; who owns which domain, and what would block a migration
stalwart-migrate status <id>	Works
stalwart-migrate report <id>	Works — prints what validation found for a run

run performs the migration, in the order preflight → stage → dump → stop → convert → recovery-mode → cutover → validate. It needs two flags: --yes (intent) and --recovery-point-confirmed (a claim that you have a snapshot or backup you have verified you can restore — this tool cannot undo a migration and will not start without it).

Start with rehearse first. It is read-only, needs no maintenance window, and tells you what run will and won't carry over.

Measured on a full migration: the store converts in seconds, and the service was down for 6 seconds end to end. Plan the window around verification, not data volume.

After cutover, run compares the migrated instance against the snapshot preflight took, and fails the command if an account that existed before is missing from it. A domain that no longer appears is reported as a warning rather than a failure: the two versions do not agree on what counts as a domain — principals on one side, Domain objects on the other — and failing a migration over that difference would abort runs that lost nothing. The service is left running either way — by that point the store has been migrated in place, so stopping it would not undo anything; your recovery point is the way back. report <run-id> prints the same finding again later. Where preflight had no admin URL to snapshot from, validation reports itself as skipped rather than passed.

Package state:

Lines are implementation only; each package carries its tests alongside.

Package	Lines	Tests
internal/stalwartapi	1456	yes
internal/backup	1333	yes
internal/preflight	1035	yes
internal/applyplan	913	yes
internal/cutover	784	yes
internal/recovery	431	yes
internal/checkpoint	406	yes
internal/validate	382	yes
internal/stage	233	yes
internal/service	201	yes
internal/plan	130	yes
internal/config	stub	—

Why not a shell script

Stalwart's 0.15 → 0.16 boundary is not a drop-in binary swap: settings move, and the data directory has to be migrated rather than merely copied. The failure mode that matters is a half-migrated mail store with no way back — which is why backup verification and checkpointing are the design centre rather than conveniences bolted on afterwards — and why the tool refuses to cut over until you confirm you have a way back.

ARCHITECTURE.md covers this in full: §1 on why a thin wrapper is insufficient, §4 on the migration phases, §5 on the checkpoint state machine, §6 on the CLI surface, and §8 on what is still open.

Build and test

go build ./...
go test ./...

Requires Go 1.26 or newer.

Trying it safely

preflight is the sensible starting point — its checks against the Stalwart installation are read-only:

sudo go run ./cmd/stalwart-migrate preflight

It still needs write access, because it records the run as a checkpoint before doing anything else:

create run: checkpoint: create run directory:
mkdir /var/lib/stalwart-migrator: permission denied

That path is checkpoint.DefaultBaseDir, a compile-time constant with no flag or environment override — so preflight needs either root or a pre-created writable /var/lib/stalwart-migrator. (run takes --work-dir for its scratch space, but that is a different directory and does not move the checkpoint store.)

rehearse is the next step, and unlike everything else here it is worth running today — see the next section.

Rehearse before you migrate

stalwart-migrate rehearse --admin-url https://mail.example.com \
    --admin-user admin --target 0.16.14

It runs preflight, dumps your settings and principals, converts them with Stalwart's own migrate_v016.py, and reports both halves of the result: the apply plan of what will carry over, and the worklist of what will not.

It copies no data, clones nothing, starts no server, and never writes to the store, so it is safe to run against production repeatedly and without a maintenance window.

It also generates a supplemental plan for the part it can rebuild automatically — currently your network listeners, which is the difference between a migrated server that answers and one that doesn't — and reports exactly how much of the worklist that covers (on a test instance: 24 of 3,505 keys, and it says so rather than implying more). Review it, then apply it after export.json:

stalwart-cli apply --file <state-dir>/runs/<run-id>/supplement.json \
    --url https://mail.example.com

The worklist is long but mostly not work, and rehearse says which is which. Measured against a real production instance, migrate_v016.py carried 219 of 12,401 settings. Of the 12,182 it left:

• 8,547 are runtime auto-ban state that repopulates itself
• 3,337 are stock spam-filter and lookup data v0.16 ships its own copies of — restoring v0.15's would revert a year of upstream updates
• ~224 were already carried another way, DKIM signatures included
• ~293 genuinely need your eyes

server.listener is in that third group only because this tool regenerates it for you; without that a migrated instance answers on no ports at all. Both outputs are preserved under <state-dir>/runs/<run-id>/ (export.json and unmigrated.txt) even though the rest of the scratch directory is cleaned up, because they are the conclusions.

This replaced an earlier run --dry-run that cloned the data directory into a sandbox and migrated the copy. That proved the store opens, at the cost of copying it twice — while the half that found every real problem needed no copy at all. ARCHITECTURE.md §4.9 has the reasoning.

Rehearse on a clone first

rehearse is read-only and stops short of the half that matters: it converts your settings but never applies them, and applying is where a real migration fails. A clone closes that gap, and on a 2.4 GB store it costs about six seconds of production downtime to build.

1. Copy the data directory with the service stopped. RocksDB is single-writer, so a hot copy may be torn — and a rehearsal on a torn store fails for reasons production never would, or passes when it should not. Stop, cp -a the data dir to the same disk, start again, archive it afterwards; the service is down only for the local copy.
2. Give the guest no route off the host. A clone of a live mail server will otherwise renew certificates for your real domains and deliver whatever is in the outbound queue. In libvirt that means a network with no <forward> element. Verify it from inside the guest rather than assuming.
3. Run the real thing: preflight, then run with --target-binary, --stalwart-cli and --migration-script pointed at locally staged copies, since an isolated guest can download nothing.
4. Snapshot the guest while it is shut down, so a failed attempt costs seconds to reset rather than a rebuild.

What that rehearsal caught, none of which the mock could express: a multi-tenant arrangement v0.16 cannot represent; --target-binary never reaching preflight, so an air-gapped host failed on a release lookup; an admin account that was a config fallback-admin and stopped working the moment the migration finished; and tenant-admin roles the converter does not restore.

Two things the isolation costs, so they are not mistaken for faults: the guest cannot fetch the v0.16 web interface, so /account/ returns 404, and certificate renewal cannot be exercised at all.

Stalwart's own converter silently drops ACME

migrate_v016.py consumes every acme.* setting and emits nothing for them. They are not reported as unmigrated either, so nothing warns you: the certificate carries over, the provider that renews it does not, and TLS keeps working until the certificate expires roughly ninety days later.

Check for acme.* in your dump before migrating, and recreate an AcmeProvider afterwards if there was one. Note that accountKey is server-set in v0.16, so the existing ACME account cannot be carried over — the server registers a new one on first issuance.

This tool does not yet generate that object for you. It should: the supplemental plan already does the equivalent for listeners.

You need a named admin account before you migrate

A config-file fallback admin will not survive the migration. If the only administrator you have is an [authentication.fallback-admin] block in config.toml — which is what stalwart --init sets up — you will come out of the migration unable to administer the server.

Create a real account in the directory, with the admin role, and confirm you can log in as it before migrating. Three separate reasons, all verified against a real 0.15.5 → 0.16.14 migration:

1. v0.16 keeps its configuration in the store, not in a file. After the migration the server is started with a config that is little more than a pointer at the data store, so the old config.toml — and the fallback-admin block inside it — is no longer read at all. That credential simply stops existing.

2. migrate_v016.py gives every migrated account the User role, whatever it held before. An account that was an administrator in v0.15 comes out authenticating normally and refused every management operation. rehearse generates the operation that restores it — but the account has to exist in the directory for there to be anything to restore.

3. The account's local part must be unambiguous. v0.16 identifies an account by local part plus domain, so if [email protected] and [email protected] both exist, this tool will refuse to restore either role rather than risk granting administrator rights to the wrong one. It says so rather than guessing; you then grant it by hand.

4. The role has to survive, not just the account. tenant-admin has no v0.16 equivalent and is not restored, so an account whose rights came only from it authenticates afterwards and is still refused management operations. Preflight cannot check this — it cannot know which roles the converter will carry across — so confirm on a clone, or immediately afterwards, that the account can still administer the server.

preflight refuses to proceed if the account you authenticate with is not in the directory, so this is caught before anything is touched rather than after the migration completes. The practical check: make sure you can authenticate to the admin API as a directory account — not as the fallback admin — that its local part is unique across your domains, and that it holds admin rights through a role other than tenant-admin.

Recovery is your job

This tool does not undo a migration. There is no rollback command. Recovery from a failed migration is your own snapshot or backup, taken by whatever method you already trust and know how to restore — a ZFS, LVM or btrfs snapshot, a VM or volume snapshot, or a restorable backup. Choosing that method, taking it, and verifying you can actually restore from it is out of scope for this tool: it does not take one, does not check that one exists, and cannot restore from one.

Cutover refuses to start until you confirm a recovery point exists. That confirmation is an acknowledgement, not a check — nothing here can verify your snapshot. Its only purpose is that nobody migrates a production mail server having never been asked the question.

Take the snapshot with the service stopped if you want a clean one. A snapshot of a running Stalwart is crash-consistent rather than clean; RocksDB will usually recover from its WAL, but "usually" is doing real work in that sentence.

Restoring from a snapshot loses mail delivered since

Reverting to any pre-migration recovery point discards mail delivered between taking it and restoring it. This is inherent to restoring a point in time and this tool cannot solve it — plan your migration window with that in mind, and consider holding inbound mail at a secondary MX for the duration if the gap matters to you.

What the tool does to make a manual restore easier

• The old binary is preserved, never deleted, next to the new one as <binary>.v<old-version> — so putting things back doesn't depend on re-downloading a specific old release under pressure.
• The original service definition is preserved as <unit>.pre-<run-id> before cutover rewrites it, so you aren't reconstructing a unit file from memory.
• The settings and principals dumps taken during backup stay on disk.
• Every artifact path and checksum is in the checkpoint, and stalwart-migrate status <run-id> prints exactly which steps completed and which failed — which is the first thing you want when deciding what to restore.

None of this is a substitute for the snapshot. It's what makes the twenty minutes after restoring one less unpleasant.

Why it works this way

An earlier version of this tool implemented rollback itself: it restored the filesystem backup, verified every restored file against a manifest, replayed SQL dumps, reinstalled the old binary, and re-validated the result. It was tested and it looked good. It was removed, because restoring bytes correctly is not the hard part — it copied contents and permissions but not ownership, so run as root it would have produced a byte-perfect, checksum-verified, root-owned data directory that Stalwart, running as its own user, could not open, and it would have reported success. A filesystem snapshot has no such failure mode, because it never lost the metadata to begin with. ARCHITECTURE.md §4.8 records the full reasoning.

License

Copyright (C) 2026 LINUXexpert-org

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/.

The full text is in LICENSE. No third-party code is vendored — this tool is standard library only, and the migrate_v016.py it downloads at runtime is Stalwart's own script, fetched rather than redistributed.