chore: Jubilee Bridge 3.20.1 changelog.

COPYING_NOTES.md

@@ -127,6 +127,7 @@ Proton Mail Bridge includes the following 3rd party software:
 * [blackfriday](https://github.com/russross/blackfriday/v2) available under [license](https://github.com/russross/blackfriday/v2/blob/master/LICENSE) 
 * [pflag](https://github.com/spf13/pflag) available under [license](https://github.com/spf13/pflag/blob/master/LICENSE) 
 * [bom](https://github.com/ssor/bom) available under [license](https://github.com/ssor/bom/blob/master/LICENSE) 
+* [objx](https://github.com/stretchr/objx) available under [license](https://github.com/stretchr/objx/blob/master/LICENSE) 
 * [golang-asm](https://github.com/twitchyliquid64/golang-asm) available under [license](https://github.com/twitchyliquid64/golang-asm/blob/master/LICENSE) 
 * [codec](https://github.com/ugorji/go/codec) available under [license](https://github.com/ugorji/go/codec/blob/master/LICENSE) 
 * [tagparser](https://github.com/vmihailenco/tagparser/v2) available under [license](https://github.com/vmihailenco/tagparser/v2/blob/master/LICENSE) 

Changelog.md

@@ -3,6 +3,33 @@
 Changelog [format](http://keepachangelog.com/en/1.0.0/)
 
 
+## Jubilee Bridge 3.20.1
+
+### Fixed
+* BRIDGE-362: Implemented logic for reconciling label conflicts.
+
+
+## Jubilee Bridge 3.20.0
+
+### Added
+* BRIDGE-348: Enable display of BYOE addresses in Bridge.
+* BRIDGE-340: Added additional logging for label operations and related bad events.
+* BRIDGE-324: Log a hash of the vault key on Bridge start.
+
+### Changed
+* BRIDGE-352: Chore: bump go to 1.24.2.
+* BRIDGE-353: Chore: update x/net package to 0.38.0.
+
+### Fixed
+* BRIDGE-351: Allow draft creation and import to BYOE addresses in combined mode.
+* BRIDGE-301: Prevent imports into non-BYOE external addresses.
+* BRIDGE-341: Replaced go-autostart with a fork to support creating autostart shortcuts in directories with Unicode characters on Windows.
+* BRIDGE-332: Strip newline characters from username and password fields in the Bridge GUI.
+* BRIDGE-336: Ensure all remote labels are verified and created in Gluon at Bridge startup.
+* BRIDGE-335: Persist the last successfully used keychain helper as a user preference on Linux.
+* BRIDGE-333: Ignore unknown label IDs during Bridge synchronization.
+
+
 ## Infinity Bridge 3.19.0
 
 ### Changed

Makefile

@@ -12,7 +12,7 @@ ROOT_DIR:=$(realpath .)
 .PHONY: build build-gui build-nogui build-launcher versioner hasher
 
 # Keep version hardcoded so app build works also without Git repository.
-BRIDGE_APP_VERSION?=3.19.0+git
+BRIDGE_APP_VERSION?=3.20.1+git
 APP_VERSION:=${BRIDGE_APP_VERSION}
 APP_FULL_NAME:=Proton Mail Bridge
 APP_VENDOR:=Proton AG

go.mod

@@ -7,7 +7,7 @@ toolchain go1.24.2
 require (
 	github.com/0xAX/notificator v0.0.0-20220220101646-ee9b8921e557
 	github.com/Masterminds/semver/v3 v3.2.0
-	github.com/ProtonMail/gluon v0.17.1-0.20250324123053-2abce471ad71
+	github.com/ProtonMail/gluon v0.17.1-0.20250527153202-a7383713882a
 	github.com/ProtonMail/go-autostart v0.0.0-20210130080809-00ed301c8e9a
 	github.com/ProtonMail/go-proton-api v0.4.1-0.20250417134000-e624a080f7ba
 	github.com/ProtonMail/gopenpgp/v2 v2.8.2-proton
@@ -114,6 +114,7 @@ require (
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/ssor/bom v0.0.0-20170718123548-6386211fdfcf // indirect
+	github.com/stretchr/objx v0.5.0 // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.2.11 // indirect
 	github.com/vmihailenco/tagparser/v2 v2.0.0 // indirect

go.sum

@@ -36,8 +36,10 @@ github.com/OneOfOne/xxhash v1.2.2/go.mod h1:HSdplMjZKSmBqAxg5vPj2TmRDmfkzw+cTzAE
 github.com/ProtonMail/bcrypt v0.0.0-20210511135022-227b4adcab57/go.mod h1:HecWFHognK8GfRDGnFQbW/LiV7A3MX3gZVs45vk5h8I=
 github.com/ProtonMail/bcrypt v0.0.0-20211005172633-e235017c1baf h1:yc9daCCYUefEs69zUkSzubzjBbL+cmOXgnmt9Fyd9ug=
 github.com/ProtonMail/bcrypt v0.0.0-20211005172633-e235017c1baf/go.mod h1:o0ESU9p83twszAU8LBeJKFAAMX14tISa0yk4Oo5TOqo=
-github.com/ProtonMail/gluon v0.17.1-0.20250324123053-2abce471ad71 h1:UC8SLrS6QbBeOUM8FJugyNoeV5gRGoQCwNePAMxuM20=
+github.com/ProtonMail/gluon v0.17.1-0.20250527093338-0b0a59c5f7d2 h1:BWo8ntIFkCeh6o2f2btbDQbUT0GYXuF5BNUOkaCbgws=
-github.com/ProtonMail/gluon v0.17.1-0.20250324123053-2abce471ad71/go.mod h1:0/c03TzZPNiSgY5UDJK1iRDkjlDPwWugxTT6et2qDu8=
+github.com/ProtonMail/gluon v0.17.1-0.20250527093338-0b0a59c5f7d2/go.mod h1:0/c03TzZPNiSgY5UDJK1iRDkjlDPwWugxTT6et2qDu8=
+github.com/ProtonMail/gluon v0.17.1-0.20250527153202-a7383713882a h1:6OhwrrhJ7/agGXC0ulIqgfzuAs33ILUs61KW5AcHcH4=
+github.com/ProtonMail/gluon v0.17.1-0.20250527153202-a7383713882a/go.mod h1:0/c03TzZPNiSgY5UDJK1iRDkjlDPwWugxTT6et2qDu8=
 github.com/ProtonMail/go-crypto v0.0.0-20230321155629-9a39f2531310/go.mod h1:8TI4H3IbrackdNgv+92dI+rhpCaLqM0IfpgCgenFvRE=
 github.com/ProtonMail/go-crypto v1.1.4-proton h1:KIo9uNlk3vzlwI7o5VjhiEjI4Ld1TDixOMnoNZyfpFE=
 github.com/ProtonMail/go-crypto v1.1.4-proton/go.mod h1:zNoyBJW3p/yVWiHNZgfTF9VsjwqYof5YY0M9kt2QaX0=
@@ -45,14 +47,6 @@ github.com/ProtonMail/go-message v0.13.1-0.20240919135104-3bc88e6a9423 h1:p8nBDx
 github.com/ProtonMail/go-message v0.13.1-0.20240919135104-3bc88e6a9423/go.mod h1:NBAn21zgCJ/52WLDyed18YvYFm5tEoeDauubFqLokM4=
 github.com/ProtonMail/go-mime v0.0.0-20230322103455-7d82a3887f2f h1:tCbYj7/299ekTTXpdwKYF8eBlsYsDVoggDAuAjoK66k=
 github.com/ProtonMail/go-mime v0.0.0-20230322103455-7d82a3887f2f/go.mod h1:gcr0kNtGBqin9zDW9GOHcVntrwnjrK+qdJ06mWYBybw=
-github.com/ProtonMail/go-proton-api v0.4.1-0.20250217140732-2e531f21de4c h1:dxnbB+ov77BDj1LC35fKZ14hLoTpU6OTpZySwxarVx0=
-github.com/ProtonMail/go-proton-api v0.4.1-0.20250217140732-2e531f21de4c/go.mod h1:RYgagBFkA3zFrSt7/vviFFwjZxBo6pGzcTwFsLwsnyc=
-github.com/ProtonMail/go-proton-api v0.4.1-0.20250409092940-13ddc20a05a1 h1:u3G9UB8prOnzOneOf0JFCIVnMRLiK4QgEpPQVu9Y8Q4=
-github.com/ProtonMail/go-proton-api v0.4.1-0.20250409092940-13ddc20a05a1/go.mod h1:RYgagBFkA3zFrSt7/vviFFwjZxBo6pGzcTwFsLwsnyc=
-github.com/ProtonMail/go-proton-api v0.4.1-0.20250409131808-0bbc8e7c32db h1:mOtbY5BB2eNr2QmbZhFn5EnsJcimTntPB6akN2r+AuE=
-github.com/ProtonMail/go-proton-api v0.4.1-0.20250409131808-0bbc8e7c32db/go.mod h1:RYgagBFkA3zFrSt7/vviFFwjZxBo6pGzcTwFsLwsnyc=
-github.com/ProtonMail/go-proton-api v0.4.1-0.20250410050801-92de6e7c8517 h1:70JoDgXxfil4hbDoYGF98rMd47Rld6wXWyFAw4uFOTY=
-github.com/ProtonMail/go-proton-api v0.4.1-0.20250410050801-92de6e7c8517/go.mod h1:RYgagBFkA3zFrSt7/vviFFwjZxBo6pGzcTwFsLwsnyc=
 github.com/ProtonMail/go-proton-api v0.4.1-0.20250417134000-e624a080f7ba h1:DFBngZ7u/f69flRFzPp6Ipo6PKEyflJlA5OCh52yDB4=
 github.com/ProtonMail/go-proton-api v0.4.1-0.20250417134000-e624a080f7ba/go.mod h1:eXIoLyIHxvPo8Kd9e1ygYIrAwbeWJhLi3vgSz2crlK4=
 github.com/ProtonMail/go-smtp v0.0.0-20231109081432-2b3d50599865 h1:EP1gnxLL5Z7xBSymE9nSTM27nRYINuvssAtDmG0suD8=
@@ -506,8 +500,6 @@ golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.7.0/go.mod h1:pYwdfH91IfpZVANVyUOhSIPZaFoJGxTFbZhFTx+dXZU=
 golang.org/x/crypto v0.14.0/go.mod h1:MVFd36DqK4CsrnJYDkBA3VC4m2GkXAM0PvzMCn4JQf4=
-golang.org/x/crypto v0.32.0 h1:euUpcYgM8WcP71gNpTqQCn6rC2t6ULUPiOzfWaXVVfc=
-golang.org/x/crypto v0.32.0/go.mod h1:ZnnJkOaASj8g0AjIduWNlq2NRxL0PlBrbKVyZ6V/Ugc=
 golang.org/x/crypto v0.36.0 h1:AnAEvhDddvBdpY+uR+MyHmuZzzNqXSe/GvuDeob5L34=
 golang.org/x/crypto v0.36.0/go.mod h1:Y4J0ReaxCR1IMaabaSMugxJES1EpwhBHhv2bDHklZvc=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
@@ -565,8 +557,6 @@ golang.org/x/net v0.8.0/go.mod h1:QVkue5JL9kW//ek3r6jTKnTFis1tRmNAW2P1shuFdJc=
 golang.org/x/net v0.9.0/go.mod h1:d48xBJpPfHeWQsugry2m+kC02ZBRGRgulfHnEXEuWns=
 golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
 golang.org/x/net v0.17.0/go.mod h1:NxSsAGuq816PNPmqtQdLE42eU2Fs7NoRIZrHJAlaCOE=
-golang.org/x/net v0.34.0 h1:Mb7Mrk043xzHgnRM88suvJFwzVrRfHEHJEl5/71CKw0=
-golang.org/x/net v0.34.0/go.mod h1:di0qlW3YNM5oh6GqDGQr92MyTozJPmybPK4Ev/Gm31k=
 golang.org/x/net v0.38.0 h1:vRMAPTMaeGqVhG5QyLJHqNDwecKTomGeqbnfZyKlBI8=
 golang.org/x/net v0.38.0/go.mod h1:ivrbrMbzFq5J41QOQh0siUuly180yBYtLp+CKbEaFx8=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
@@ -583,8 +573,6 @@ golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.10.0 h1:3NQrjDixjgGwUOCaF8w2+VYHv0Ve/vGYSbdkTa98gmQ=
-golang.org/x/sync v0.10.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sync v0.12.0 h1:MHc5BpPuC30uJk597Ri8TV3CNZcTLu6B6z4lJy+g6Jw=
 golang.org/x/sync v0.12.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
 golang.org/x/sys v0.0.0-20180823144017-11551d06cbcc/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
@@ -625,8 +613,6 @@ golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.29.0 h1:TPYlXGxvx1MGTn2GiZDhnjPA9wZzZeGKHHmKhHYvgaU=
-golang.org/x/sys v0.29.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.31.0 h1:ioabZlmFYtWhL+TRYpcnNlLwhyxaM9kWTDEmfnprqik=
 golang.org/x/sys v0.31.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
@@ -648,8 +634,6 @@ golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/text v0.8.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
 golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
 golang.org/x/text v0.13.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
-golang.org/x/text v0.21.0 h1:zyQAAkrwaneQ066sspRyJaG9VNi/YJ1NfzcGB3hZ/qo=
-golang.org/x/text v0.21.0/go.mod h1:4IBbMaMmOPCJ8SecivzSH54+73PCFmPWxNTLm+vZkEQ=
 golang.org/x/text v0.23.0 h1:D71I7dUrlY+VX0gQShAThNGHFxZ13dGLBHQLVl1mJlY=
 golang.org/x/text v0.23.0/go.mod h1:/BLNzu4aZCJ1+kcD0DNRotWKage4q2rGVAg4o22unh4=
 golang.org/x/time v0.0.0-20181108054448-85acf8d2951c/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=

internal/dialer/dialer_pinning_test.go

@@ -96,7 +96,7 @@ func TestTLSSignedCertTrustedPublicKey(t *testing.T) {
 
 	_, dialer, _, checker, _ := createClientWithPinningDialer("")
 	copyTrustedPins(checker)
-	checker.trustedPins = append(checker.trustedPins, `pin-sha256="hgraU1+uoS6kjiJaH5G+BiqQoyiIml1Nat+2FiUAcII="`)
+	checker.trustedPins = append(checker.trustedPins, `pin-sha256="FlvTPG/nIMKtOj9nelnEjujwSZ5EDyfiKYxZgbXREls="`)
 	_, err := dialer.DialTLSContext(context.Background(), "tcp", "rsa4096.badssl.com:443")
 	r.NoError(t, err, "expected dial to succeed because public key is known and cert is signed by CA")
 }

internal/services/imapservice/conflicts.go

@@ -0,0 +1,211 @@
+// Copyright (c) 2025 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge 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.
+//
+// Proton Mail Bridge 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 Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package imapservice
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+
+	"github.com/ProtonMail/gluon/db"
+	"github.com/ProtonMail/gluon/imap"
+	"github.com/ProtonMail/gluon/reporter"
+	"github.com/ProtonMail/go-proton-api"
+	"github.com/ProtonMail/proton-bridge/v3/internal/unleash"
+	"github.com/sirupsen/logrus"
+)
+
+type GluonLabelNameProvider interface {
+	GetUserMailboxByName(ctx context.Context, addrID string, labelName []string) (imap.MailboxData, error)
+}
+
+type gluonIDProvider interface {
+	GetGluonID(addrID string) (string, bool)
+}
+
+type sentryReporter interface {
+	ReportMessageWithContext(string, reporter.Context) error
+}
+
+type apiClient interface {
+	GetLabel(ctx context.Context, labelID string, labelTypes ...proton.LabelType) (proton.Label, error)
+}
+
+type mailboxFetcherFn func(ctx context.Context, label proton.Label) (imap.MailboxData, error)
+
+type LabelConflictManager struct {
+	gluonLabelNameProvider GluonLabelNameProvider
+	gluonIDProvider        gluonIDProvider
+	client                 apiClient
+	reporter               sentryReporter
+	getFeatureFlagValueFn  unleash.GetFlagValueFn
+}
+
+func NewLabelConflictManager(
+	gluonLabelNameProvider GluonLabelNameProvider,
+	gluonIDProvider gluonIDProvider,
+	client apiClient,
+	reporter sentryReporter,
+	getFeatureFlagValueFn unleash.GetFlagValueFn) *LabelConflictManager {
+	return &LabelConflictManager{
+		gluonLabelNameProvider: gluonLabelNameProvider,
+		gluonIDProvider:        gluonIDProvider,
+		client:                 client,
+		reporter:               reporter,
+		getFeatureFlagValueFn:  getFeatureFlagValueFn,
+	}
+}
+
+func (m *LabelConflictManager) generateMailboxFetcher(connectors []*Connector) mailboxFetcherFn {
+	return func(ctx context.Context, label proton.Label) (imap.MailboxData, error) {
+		for _, updateCh := range connectors {
+			addrID, ok := m.gluonIDProvider.GetGluonID(updateCh.addrID)
+			if !ok {
+				continue
+			}
+			return m.gluonLabelNameProvider.GetUserMailboxByName(ctx, addrID, GetMailboxName(label))
+		}
+		return imap.MailboxData{}, errors.New("no gluon connectors found")
+	}
+}
+
+type LabelConflictResolver interface {
+	ResolveConflict(ctx context.Context, label proton.Label, visited map[string]bool) (func() []imap.Update, error)
+}
+type labelConflictResolverImpl struct {
+	mailboxFetch mailboxFetcherFn
+	client       apiClient
+	reporter     sentryReporter
+}
+
+type nullLabelConflictResolverImpl struct {
+}
+
+func (r *nullLabelConflictResolverImpl) ResolveConflict(_ context.Context, _ proton.Label, _ map[string]bool) (func() []imap.Update, error) {
+	return func() []imap.Update {
+		return []imap.Update{}
+	}, nil
+}
+
+func (m *LabelConflictManager) NewConflictResolver(connectors []*Connector) LabelConflictResolver {
+	if m.getFeatureFlagValueFn(unleash.LabelConflictResolverDisabled) {
+		return &nullLabelConflictResolverImpl{}
+	}
+
+	return &labelConflictResolverImpl{
+		mailboxFetch: m.generateMailboxFetcher(connectors),
+		client:       m.client,
+		reporter:     m.reporter,
+	}
+}
+
+func (r *labelConflictResolverImpl) ResolveConflict(ctx context.Context, label proton.Label, visited map[string]bool) (func() []imap.Update, error) {
+	var updateFns []func() []imap.Update
+
+	// There's a cycle, such as in a label swap operation, we'll need to temporarily rename the label.
+	// The change will be overwritten by one of the previous recursive calls.
+	if visited[label.ID] {
+		fn := func() []imap.Update {
+			return []imap.Update{newMailboxUpdatedOrCreated(imap.MailboxID(label.ID), getMailboxNameWithTempPrefix(label))}
+		}
+		updateFns = append(updateFns, fn)
+		return combineIMAPUpdateFns(updateFns), nil
+	}
+	visited[label.ID] = true
+
+	// Fetch the gluon mailbox data and verify whether there are conflicts with the name.
+	mailboxData, err := r.mailboxFetch(ctx, label)
+	if err != nil {
+		// Name is free, create the mailbox.
+		if db.IsErrNotFound(err) {
+			fn := func() []imap.Update {
+				return []imap.Update{newMailboxUpdatedOrCreated(imap.MailboxID(label.ID), GetMailboxName(label))}
+			}
+			updateFns = append(updateFns, fn)
+			return combineIMAPUpdateFns(updateFns), nil
+		}
+		return combineIMAPUpdateFns(updateFns), err
+	}
+
+	// Verify whether the label name corresponds to the same label ID. If true terminate, we don't need to update.
+	if mailboxData.RemoteID == label.ID {
+		return combineIMAPUpdateFns(updateFns), nil
+	}
+
+	// If the label name belongs to some other label ID. Fetch it's state from the remote.
+	conflictingLabel, err := r.client.GetLabel(ctx, mailboxData.RemoteID, proton.LabelTypeFolder, proton.LabelTypeLabel)
+	if err != nil {
+		// If it's not present on the remote we should delete it. And create the new label.
+		if errors.Is(err, proton.ErrNoSuchLabel) {
+			fn := func() []imap.Update {
+				return []imap.Update{
+					imap.NewMailboxDeleted(imap.MailboxID(mailboxData.RemoteID)),
+					newMailboxUpdatedOrCreated(imap.MailboxID(label.ID), GetMailboxName(label)),
+				}
+			}
+			updateFns = append(updateFns, fn)
+			return combineIMAPUpdateFns(updateFns), nil
+		}
+		return combineIMAPUpdateFns(updateFns), err
+	}
+
+	// Check if the conflicting label name has changed. If not, then this is a BE inconsistency.
+	if compareLabelNames(GetMailboxName(conflictingLabel), mailboxData.BridgeName) {
+		if err := r.reporter.ReportMessageWithContext("Unexpected label conflict", reporter.Context{
+			"labelID":            label.ID,
+			"conflictingLabelID": conflictingLabel.ID,
+		}); err != nil {
+			logrus.WithError(err).Error("Failed to report update error")
+		}
+
+		err := fmt.Errorf("unexpected label conflict: the name of label ID %s is already used by label ID %s", label.ID, conflictingLabel.ID)
+		return combineIMAPUpdateFns(updateFns), err
+	}
+
+	// The name of the conflicting label has changed on the remote. We need to verify that the new name does not conflict with anything else.
+	// Thus, a recursive check can be performed.
+	childUpdateFns, err := r.ResolveConflict(ctx, conflictingLabel, visited)
+	if err != nil {
+		return combineIMAPUpdateFns(updateFns), err
+	}
+	updateFns = append(updateFns, childUpdateFns)
+
+	fn := func() []imap.Update {
+		return []imap.Update{newMailboxUpdatedOrCreated(imap.MailboxID(label.ID), GetMailboxName(label))}
+	}
+	updateFns = append(updateFns, fn)
+
+	return combineIMAPUpdateFns(updateFns), nil
+}
+
+func combineIMAPUpdateFns(updateFunctions []func() []imap.Update) func() []imap.Update {
+	return func() []imap.Update {
+		var updates []imap.Update
+		for _, fn := range updateFunctions {
+			updates = append(updates, fn()...)
+		}
+		return updates
+	}
+}
+
+func compareLabelNames(labelName1, labelName2 []string) bool {
+	name1 := strings.Join(labelName1, "")
+	name2 := strings.Join(labelName2, "")
+	return name1 == name2
+}

internal/services/imapservice/conflicts_test.go

@@ -0,0 +1,682 @@
+// Copyright (c) 2025 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge 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.
+//
+// Proton Mail Bridge 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 Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package imapservice_test
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/ProtonMail/gluon/db"
+	"github.com/ProtonMail/gluon/imap"
+	"github.com/ProtonMail/gluon/reporter"
+	"github.com/ProtonMail/go-proton-api"
+	"github.com/ProtonMail/proton-bridge/v3/internal/services/imapservice"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+)
+
+func getFeatureFlagValueMock(_ string) bool {
+	return false
+}
+
+type mockLabelNameProvider struct {
+	mock.Mock
+}
+
+func (m *mockLabelNameProvider) GetUserMailboxByName(ctx context.Context, addrID string, labelName []string) (imap.MailboxData, error) {
+	args := m.Called(ctx, addrID, labelName)
+	v, ok := args.Get(0).(imap.MailboxData)
+	if !ok {
+		return imap.MailboxData{}, fmt.Errorf("failed to assert type")
+	}
+	return v, args.Error(1)
+}
+
+type mockIDProvider struct {
+	mock.Mock
+}
+
+func (m *mockIDProvider) GetGluonID(addrID string) (string, bool) {
+	args := m.Called(addrID)
+	return args.String(0), args.Bool(1)
+}
+
+type mockAPIClient struct {
+	mock.Mock
+}
+
+func (m *mockAPIClient) GetLabel(ctx context.Context, id string, types ...proton.LabelType) (proton.Label, error) {
+	args := m.Called(ctx, id, types)
+	v, ok := args.Get(0).(proton.Label)
+	if !ok {
+		return proton.Label{}, fmt.Errorf("failed to assert type")
+	}
+	return v, args.Error(1)
+}
+
+type mockReporter struct {
+	mock.Mock
+}
+
+func (m *mockReporter) ReportMessageWithContext(msg string, ctx reporter.Context) error {
+	args := m.Called(msg, ctx)
+	return args.Error(0)
+}
+
+func TestResolveConflict_UnexpectedLabelConflict(t *testing.T) {
+	ctx := context.Background()
+	label := proton.Label{
+		ID:   "label-1",
+		Path: []string{"Work"},
+		Type: proton.LabelTypeLabel,
+	}
+	conflictingLabel := proton.Label{
+		ID:   "label-2",
+		Path: []string{"Work"},
+		Type: proton.LabelTypeLabel,
+	}
+	conflictMbox := imap.MailboxData{
+		RemoteID:   "label-2",
+		BridgeName: []string{"Labels", "Work"},
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockIDProvider := new(mockIDProvider)
+	mockClient := new(mockAPIClient)
+	mockReporter := new(mockReporter)
+
+	mockLabelProvider.On("GetUserMailboxByName", mock.Anything, "gluon-id", imapservice.GetMailboxName(label)).
+		Return(conflictMbox, nil)
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id", true)
+	mockClient.On("GetLabel", mock.Anything, "label-2", mock.Anything).
+		Return(conflictingLabel, nil)
+	mockReporter.On("ReportMessageWithContext", "Unexpected label conflict", mock.Anything).
+		Return(nil)
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	resolver := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock).
+		NewConflictResolver([]*imapservice.Connector{connector})
+
+	visited := make(map[string]bool)
+	_, err := resolver.ResolveConflict(ctx, label, visited)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "unexpected label conflict")
+}
+
+func TestResolveDiscrepancy_LabelDoesNotExist(t *testing.T) {
+	ctx := context.Background()
+	label := proton.Label{
+		ID:   "label-id-1",
+		Name: "Inbox",
+		Type: proton.LabelTypeLabel,
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockIDProvider := new(mockIDProvider)
+	mockClient := new(mockAPIClient)
+	mockReporter := new(mockReporter)
+
+	mockLabelProvider.On("GetUserMailboxByName", mock.Anything, "gluon-id-1", imapservice.GetMailboxName(label)).
+		Return(imap.MailboxData{}, db.ErrNotFound)
+
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id-1", true)
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	connectors := []*imapservice.Connector{connector}
+
+	manager := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock)
+	resolver := manager.NewConflictResolver(connectors)
+
+	visited := make(map[string]bool)
+	fn, err := resolver.ResolveConflict(ctx, label, visited)
+
+	assert.NoError(t, err)
+	updates := fn()
+	assert.Len(t, updates, 1)
+	muc, ok := updates[0].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(label.ID), muc.Mailbox.ID)
+}
+
+func TestResolveConflict_MailboxFetchError(t *testing.T) {
+	ctx := context.Background()
+	label := proton.Label{
+		ID:   "111",
+		Path: []string{"Work"},
+		Type: proton.LabelTypeLabel,
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockIDProvider := new(mockIDProvider)
+	mockClient := new(mockAPIClient)
+	mockReporter := new(mockReporter)
+
+	mockLabelProvider.On("GetUserMailboxByName", mock.Anything, "gluon-id", imapservice.GetMailboxName(label)).
+		Return(imap.MailboxData{}, errors.New("database connection error"))
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id", true)
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	resolver := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock).
+		NewConflictResolver([]*imapservice.Connector{connector})
+
+	visited := make(map[string]bool)
+	_, err := resolver.ResolveConflict(ctx, label, visited)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "database connection error")
+}
+
+func TestResolveDiscrepancy_ConflictingLabelDeletedRemotely(t *testing.T) {
+	ctx := context.Background()
+	label := proton.Label{
+		ID:   "label-new",
+		Path: []string{"Work"},
+		Type: proton.LabelTypeLabel,
+	}
+	conflictMbox := imap.MailboxData{
+		RemoteID:   "label-old",
+		BridgeName: []string{"Labels", "Work"},
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockIDProvider := new(mockIDProvider)
+	mockClient := new(mockAPIClient)
+	mockReporter := new(mockReporter)
+
+	mockLabelProvider.On("GetUserMailboxByName", mock.Anything, "gluon-id-1", imapservice.GetMailboxName(label)).
+		Return(conflictMbox, nil)
+
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id-1", true)
+
+	mockClient.On("GetLabel", mock.Anything, "label-old", mock.Anything).
+		Return(proton.Label{}, proton.ErrNoSuchLabel)
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	connectors := []*imapservice.Connector{connector}
+
+	manager := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock)
+	resolver := manager.NewConflictResolver(connectors)
+
+	visited := make(map[string]bool)
+	fn, err := resolver.ResolveConflict(ctx, label, visited)
+
+	assert.NoError(t, err)
+	updates := fn()
+	assert.Len(t, updates, 2)
+	deleted, ok := updates[0].(*imap.MailboxDeleted)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID("label-old"), deleted.MailboxID)
+
+	updated, ok := updates[1].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, "Work", updated.Mailbox.Name[len(updated.Mailbox.Name)-1])
+}
+
+func TestResolveDiscrepancy_LabelAlreadyCorrect(t *testing.T) {
+	ctx := context.Background()
+	label := proton.Label{
+		ID:   "label-id-1",
+		Name: "Personal",
+		Type: proton.LabelTypeLabel,
+	}
+	mbox := imap.MailboxData{
+		RemoteID:   "label-id-1",
+		BridgeName: []string{"Labels", "Personal"},
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockIDProvider := new(mockIDProvider)
+	mockClient := new(mockAPIClient)
+	mockReporter := new(mockReporter)
+
+	mockLabelProvider.On("GetUserMailboxByName", mock.Anything, "gluon-id-1", imapservice.GetMailboxName(label)).
+		Return(mbox, nil)
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id-1", true)
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	connectors := []*imapservice.Connector{connector}
+
+	manager := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock)
+	resolver := manager.NewConflictResolver(connectors)
+
+	visited := make(map[string]bool)
+	fn, err := resolver.ResolveConflict(ctx, label, visited)
+
+	assert.NoError(t, err)
+	assert.Len(t, fn(), 0)
+}
+
+func TestResolveConflict_DeepNestedPath(t *testing.T) {
+	ctx := context.Background()
+	label := proton.Label{
+		ID:   "111",
+		Path: []string{"Level1", "Level2", "Level3", "DeepFolder"},
+		Type: proton.LabelTypeFolder,
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockIDProvider := new(mockIDProvider)
+	mockClient := new(mockAPIClient)
+	mockReporter := new(mockReporter)
+
+	mockLabelProvider.On("GetUserMailboxByName", mock.Anything, "gluon-id", imapservice.GetMailboxName(label)).
+		Return(imap.MailboxData{}, db.ErrNotFound)
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id", true)
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	resolver := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock).
+		NewConflictResolver([]*imapservice.Connector{connector})
+
+	visited := make(map[string]bool)
+	fn, err := resolver.ResolveConflict(ctx, label, visited)
+
+	assert.NoError(t, err)
+	updates := fn()
+	assert.Len(t, updates, 1)
+
+	updated, ok := updates[0].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID("111"), updated.Mailbox.ID)
+	expectedName := imapservice.GetMailboxName(label)
+	assert.Equal(t, expectedName, updated.Mailbox.Name)
+}
+
+func TestResolveLabelDiscrepancy_LabelSwap(t *testing.T) {
+	apiLabels := []proton.Label{
+		{
+			ID:   "111",
+			Path: []string{"X"},
+			Type: proton.LabelTypeLabel,
+		},
+		{
+			ID:   "222",
+			Path: []string{"Y"},
+			Type: proton.LabelTypeLabel,
+		},
+	}
+
+	gluonLabels := []imap.MailboxData{
+		{
+			RemoteID:   "111",
+			BridgeName: []string{"Labels", "Y"},
+		},
+		{
+			RemoteID:   "222",
+			BridgeName: []string{"Labels", "X"},
+		},
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockClient := new(mockAPIClient)
+	mockIDProvider := new(mockIDProvider)
+	mockReporter := new(mockReporter)
+
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id-1", true)
+
+	for _, mbox := range gluonLabels {
+		mockLabelProvider.
+			On("GetUserMailboxByName", mock.Anything, "gluon-id-1", mbox.BridgeName).
+			Return(mbox, nil)
+	}
+
+	for _, label := range apiLabels {
+		mockClient.
+			On("GetLabel", mock.Anything, label.ID, []proton.LabelType{proton.LabelTypeFolder, proton.LabelTypeLabel}).
+			Return(label, nil)
+	}
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	connectors := []*imapservice.Connector{connector}
+
+	manager := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock)
+	resolver := manager.NewConflictResolver(connectors)
+
+	visited := make(map[string]bool)
+	fn, err := resolver.ResolveConflict(context.Background(), apiLabels[0], visited)
+	require.NoError(t, err)
+
+	updates := fn()
+	assert.NotEmpty(t, updates)
+	assert.Equal(t, 3, len(updates)) // We expect three calls to be made for a swap operation.
+
+	updateOne, ok := updates[0].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[0].ID), updateOne.Mailbox.ID)
+	assert.Equal(t, "tmp_X", updateOne.Mailbox.Name[len(updateOne.Mailbox.Name)-1])
+
+	updateTwo, ok := updates[1].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[1].ID), updateTwo.Mailbox.ID)
+	assert.Equal(t, "Y", updateTwo.Mailbox.Name[len(updateTwo.Mailbox.Name)-1])
+
+	updateThree, ok := updates[2].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[0].ID), updateThree.Mailbox.ID)
+	assert.Equal(t, "X", updateThree.Mailbox.Name[len(updateThree.Mailbox.Name)-1])
+}
+
+func TestResolveLabelDiscrepancy_LabelSwapExtended(t *testing.T) {
+	apiLabels := []proton.Label{
+		{
+			ID:   "111",
+			Path: []string{"X"},
+			Type: proton.LabelTypeLabel,
+		},
+		{
+			ID:   "222",
+			Path: []string{"Y"},
+			Type: proton.LabelTypeLabel,
+		},
+		{
+			ID:   "333",
+			Path: []string{"Z"},
+			Type: proton.LabelTypeLabel,
+		},
+		{
+			ID:   "444",
+			Path: []string{"D"},
+			Type: proton.LabelTypeLabel,
+		},
+	}
+
+	gluonLabels := []imap.MailboxData{
+		{
+			RemoteID:   "111",
+			BridgeName: []string{"Labels", "D"},
+		},
+		{
+			RemoteID:   "222",
+			BridgeName: []string{"Labels", "Z"},
+		},
+		{
+			RemoteID:   "333",
+			BridgeName: []string{"Labels", "Y"},
+		},
+		{
+			RemoteID:   "444",
+			BridgeName: []string{"Labels", "X"},
+		},
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockClient := new(mockAPIClient)
+	mockIDProvider := new(mockIDProvider)
+	mockReporter := new(mockReporter)
+
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id-1", true)
+
+	for _, mbox := range gluonLabels {
+		mockLabelProvider.
+			On("GetUserMailboxByName", mock.Anything, "gluon-id-1", mbox.BridgeName).
+			Return(mbox, nil)
+	}
+
+	for _, label := range apiLabels {
+		mockClient.
+			On("GetLabel", mock.Anything, label.ID, []proton.LabelType{proton.LabelTypeFolder, proton.LabelTypeLabel}).
+			Return(label, nil)
+	}
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	connectors := []*imapservice.Connector{connector}
+
+	manager := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock)
+	resolver := manager.NewConflictResolver(connectors)
+
+	fn, err := resolver.ResolveConflict(context.Background(), apiLabels[0], make(map[string]bool))
+	require.NoError(t, err)
+
+	updates := fn()
+	assert.NotEmpty(t, updates)
+	// Three calls yet again for a swap operation.
+	assert.Equal(t, 3, len(updates))
+	updateOne, ok := updates[0].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[0].ID), updateOne.Mailbox.ID)
+	assert.Equal(t, "tmp_X", updateOne.Mailbox.Name[len(updateOne.Mailbox.Name)-1])
+
+	updateTwo, ok := updates[1].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[3].ID), updateTwo.Mailbox.ID)
+	assert.Equal(t, "D", updateTwo.Mailbox.Name[len(updateTwo.Mailbox.Name)-1])
+
+	updateThree, ok := updates[2].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[0].ID), updateThree.Mailbox.ID)
+	assert.Equal(t, "X", updateThree.Mailbox.Name[len(updateThree.Mailbox.Name)-1])
+
+	// Fix the secondary swap.
+	fn, err = resolver.ResolveConflict(context.Background(), apiLabels[1], make(map[string]bool))
+	require.NoError(t, err)
+
+	updates = fn()
+	assert.Equal(t, 3, len(updates))
+	updateOne, ok = updates[0].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[1].ID), updateOne.Mailbox.ID)
+	assert.Equal(t, "tmp_Y", updateOne.Mailbox.Name[len(updateOne.Mailbox.Name)-1])
+
+	updateTwo, ok = updates[1].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[2].ID), updateTwo.Mailbox.ID)
+	assert.Equal(t, "Z", updateTwo.Mailbox.Name[len(updateTwo.Mailbox.Name)-1])
+
+	updateThree, ok = updates[2].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[1].ID), updateThree.Mailbox.ID)
+	assert.Equal(t, "Y", updateThree.Mailbox.Name[len(updateThree.Mailbox.Name)-1])
+}
+
+func TestResolveLabelDiscrepancy_LabelSwapCyclic(t *testing.T) {
+	apiLabels := []proton.Label{
+		{ID: "111", Path: []string{"A"}, Type: proton.LabelTypeLabel},
+		{ID: "222", Path: []string{"B"}, Type: proton.LabelTypeLabel},
+		{ID: "333", Path: []string{"C"}, Type: proton.LabelTypeLabel},
+		{ID: "444", Path: []string{"D"}, Type: proton.LabelTypeLabel},
+	}
+
+	gluonLabels := []imap.MailboxData{
+		{RemoteID: "111", BridgeName: []string{"Labels", "D"}}, // A <- D
+		{RemoteID: "222", BridgeName: []string{"Labels", "A"}}, // B <- A
+		{RemoteID: "333", BridgeName: []string{"Labels", "B"}}, // C <- B
+		{RemoteID: "444", BridgeName: []string{"Labels", "C"}}, // D <- C
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockClient := new(mockAPIClient)
+	mockIDProvider := new(mockIDProvider)
+	mockReporter := new(mockReporter)
+
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id-1", true)
+
+	for _, mbox := range gluonLabels {
+		mockLabelProvider.
+			On("GetUserMailboxByName", mock.Anything, "gluon-id-1", mbox.BridgeName).
+			Return(mbox, nil)
+	}
+
+	for _, label := range apiLabels {
+		mockClient.
+			On("GetLabel", mock.Anything, label.ID, []proton.LabelType{proton.LabelTypeFolder, proton.LabelTypeLabel}).
+			Return(label, nil)
+	}
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	connectors := []*imapservice.Connector{connector}
+
+	manager := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock)
+	resolver := manager.NewConflictResolver(connectors)
+
+	fn, err := resolver.ResolveConflict(context.Background(), apiLabels[0], make(map[string]bool))
+	require.NoError(t, err)
+
+	updates := fn()
+	assert.NotEmpty(t, updates)
+	assert.Equal(t, 5, len(updates))
+
+	updateOne, ok := updates[0].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[0].ID), updateOne.Mailbox.ID)
+	assert.Equal(t, "tmp_A", updateOne.Mailbox.Name[len(updateOne.Mailbox.Name)-1])
+
+	updateTwo, ok := updates[1].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[3].ID), updateTwo.Mailbox.ID)
+	assert.Equal(t, "D", updateTwo.Mailbox.Name[len(updateTwo.Mailbox.Name)-1])
+
+	updateThree, ok := updates[2].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[2].ID), updateThree.Mailbox.ID)
+	assert.Equal(t, "C", updateThree.Mailbox.Name[len(updateThree.Mailbox.Name)-1])
+
+	updateFour, ok := updates[3].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[1].ID), updateFour.Mailbox.ID)
+	assert.Equal(t, "B", updateFour.Mailbox.Name[len(updateFour.Mailbox.Name)-1])
+
+	updateFive, ok := updates[4].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[0].ID), updateFive.Mailbox.ID)
+	assert.Equal(t, "A", updateFive.Mailbox.Name[len(updateFive.Mailbox.Name)-1])
+}
+
+func TestResolveLabelDiscrepancy_LabelSwapCyclicWithDeletedLabel(t *testing.T) {
+	apiLabels := []proton.Label{
+		{ID: "111", Path: []string{"A"}, Type: proton.LabelTypeLabel},
+		{ID: "333", Path: []string{"C"}, Type: proton.LabelTypeLabel},
+		{ID: "444", Path: []string{"D"}, Type: proton.LabelTypeLabel},
+	}
+
+	gluonLabels := []imap.MailboxData{
+		{RemoteID: "111", BridgeName: []string{"Labels", "D"}},
+		{RemoteID: "222", BridgeName: []string{"Labels", "A"}},
+		{RemoteID: "333", BridgeName: []string{"Labels", "B"}},
+		{RemoteID: "444", BridgeName: []string{"Labels", "C"}},
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockClient := new(mockAPIClient)
+	mockIDProvider := new(mockIDProvider)
+	mockReporter := new(mockReporter)
+
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id-1", true)
+
+	for _, mbox := range gluonLabels {
+		mockLabelProvider.
+			On("GetUserMailboxByName", mock.Anything, "gluon-id-1", mbox.BridgeName).
+			Return(mbox, nil)
+	}
+
+	for _, label := range apiLabels {
+		mockClient.
+			On("GetLabel", mock.Anything, label.ID, []proton.LabelType{proton.LabelTypeFolder, proton.LabelTypeLabel}).
+			Return(label, nil)
+	}
+	mockClient.On("GetLabel", mock.Anything, "222", []proton.LabelType{proton.LabelTypeFolder, proton.LabelTypeLabel}).Return(proton.Label{}, proton.ErrNoSuchLabel)
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	connectors := []*imapservice.Connector{connector}
+
+	manager := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagValueMock)
+	resolver := manager.NewConflictResolver(connectors)
+
+	fn, err := resolver.ResolveConflict(context.Background(), apiLabels[2], make(map[string]bool))
+	require.NoError(t, err)
+
+	updates := fn()
+	assert.NotEmpty(t, updates)
+	assert.Equal(t, 3, len(updates))
+
+	updateOne, ok := updates[0].(*imap.MailboxDeleted)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID("222"), updateOne.MailboxID)
+
+	updateTwo, ok := updates[1].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[0].ID), updateTwo.Mailbox.ID)
+	assert.Equal(t, "A", updateTwo.Mailbox.Name[len(updateTwo.Mailbox.Name)-1])
+
+	updateThree, ok := updates[2].(*imap.MailboxUpdatedOrCreated)
+	assert.True(t, ok)
+	assert.Equal(t, imap.MailboxID(apiLabels[2].ID), updateThree.Mailbox.ID)
+	assert.Equal(t, "D", updateThree.Mailbox.Name[len(updateThree.Mailbox.Name)-1])
+}
+
+func TestResolveLabelDiscrepancy_LabelSwapCyclicWithDeletedLabel_KillSwitchEnabled(t *testing.T) {
+	apiLabels := []proton.Label{
+		{ID: "111", Path: []string{"A"}, Type: proton.LabelTypeLabel},
+		{ID: "333", Path: []string{"C"}, Type: proton.LabelTypeLabel},
+		{ID: "444", Path: []string{"D"}, Type: proton.LabelTypeLabel},
+	}
+
+	gluonLabels := []imap.MailboxData{
+		{RemoteID: "111", BridgeName: []string{"Labels", "D"}},
+		{RemoteID: "222", BridgeName: []string{"Labels", "A"}},
+		{RemoteID: "333", BridgeName: []string{"Labels", "B"}},
+		{RemoteID: "444", BridgeName: []string{"Labels", "C"}},
+	}
+
+	mockLabelProvider := new(mockLabelNameProvider)
+	mockClient := new(mockAPIClient)
+	mockIDProvider := new(mockIDProvider)
+	mockReporter := new(mockReporter)
+
+	mockIDProvider.On("GetGluonID", "addr-1").Return("gluon-id-1", true)
+
+	for _, mbox := range gluonLabels {
+		mockLabelProvider.
+			On("GetUserMailboxByName", mock.Anything, "gluon-id-1", mbox.BridgeName).
+			Return(mbox, nil)
+	}
+
+	for _, label := range apiLabels {
+		mockClient.
+			On("GetLabel", mock.Anything, label.ID, []proton.LabelType{proton.LabelTypeFolder, proton.LabelTypeLabel}).
+			Return(label, nil)
+	}
+	mockClient.On("GetLabel", mock.Anything, "222", []proton.LabelType{proton.LabelTypeFolder, proton.LabelTypeLabel}).Return(proton.Label{}, proton.ErrNoSuchLabel)
+
+	connector := &imapservice.Connector{}
+	connector.SetAddrIDTest("addr-1")
+	connectors := []*imapservice.Connector{connector}
+
+	getFeatureFlagFn := func(_ string) bool {
+		return true
+	}
+
+	manager := imapservice.NewLabelConflictManager(mockLabelProvider, mockIDProvider, mockClient, mockReporter, getFeatureFlagFn)
+	resolver := manager.NewConflictResolver(connectors)
+
+	fn, err := resolver.ResolveConflict(context.Background(), apiLabels[2], make(map[string]bool))
+	require.NoError(t, err)
+
+	updates := fn()
+	assert.Empty(t, updates)
+}

internal/services/imapservice/connector.go

@@ -800,8 +800,10 @@ func (s *Connector) createDraftWithParser(ctx context.Context, parser *parser.Pa
 	return draft, nil
 }
 
-func (s *Connector) publishUpdate(_ context.Context, update imap.Update) {
+func (s *Connector) publishUpdate(_ context.Context, updates ...imap.Update) {
-	s.updateCh.Enqueue(update)
+	for _, update := range updates {
+		s.updateCh.Enqueue(update)
+	}
 }
 
 func fixGODT3003Labels(
@@ -903,3 +905,7 @@ func (s *Connector) getSenderProtonAddress(p *parser.Parser) (proton.Address, er
 
 	return addressList[index], nil
 }
+
+func (s *Connector) SetAddrIDTest(addrID string) {
+	s.addrID = addrID
+}

internal/services/imapservice/imap_updates.go

@@ -102,6 +102,16 @@ func newMailboxCreatedUpdate(labelID imap.MailboxID, labelName []string) *imap.M
 	})
 }
 
+func newMailboxUpdatedOrCreated(labelID imap.MailboxID, labelName []string) *imap.MailboxUpdatedOrCreated {
+	return imap.NewMailboxUpdatedOrCreated(imap.Mailbox{
+		ID:             labelID,
+		Name:           labelName,
+		Flags:          defaultMailboxFlags(),
+		PermanentFlags: defaultMailboxPermanentFlags(),
+		Attributes:     imap.NewFlagSet(),
+	})
+}
+
 func GetMailboxName(label proton.Label) []string {
 	var name []string
 
@@ -122,3 +132,12 @@ func GetMailboxName(label proton.Label) []string {
 
 	return name
 }
+
+func nameWithTempPrefix(path []string) []string {
+	path[len(path)-1] = "tmp_" + path[len(path)-1]
+	return path
+}
+
+func getMailboxNameWithTempPrefix(label proton.Label) []string {
+	return nameWithTempPrefix(GetMailboxName(label))
+}

internal/services/imapservice/server_manager.go

@@ -21,6 +21,7 @@ import (
 	"context"
 
 	"github.com/ProtonMail/gluon/connector"
+	"github.com/ProtonMail/gluon/imap"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/syncservice"
 )
 
@@ -36,6 +37,8 @@ type IMAPServerManager interface {
 	RemoveIMAPUser(ctx context.Context, deleteData bool, provider GluonIDProvider, addrID ...string) error
 
 	LogRemoteLabelIDs(ctx context.Context, provider GluonIDProvider, addrID ...string) error
+
+	GetUserMailboxByName(ctx context.Context, addrID string, mailboxName []string) (imap.MailboxData, error)
 }
 
 type NullIMAPServerManager struct{}
@@ -67,6 +70,10 @@ func (n NullIMAPServerManager) LogRemoteLabelIDs(
 	return nil
 }
 
+func (n NullIMAPServerManager) GetUserMailboxByName(_ context.Context, _ string, _ []string) (imap.MailboxData, error) {
+	return imap.MailboxData{}, nil
+}
+
 func NewNullIMAPServerManager() *NullIMAPServerManager {
 	return &NullIMAPServerManager{}
 }

internal/services/imapservice/service.go

@@ -36,6 +36,7 @@ import (
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/syncservice"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/userevents"
 	"github.com/ProtonMail/proton-bridge/v3/internal/services/useridentity"
+	"github.com/ProtonMail/proton-bridge/v3/internal/unleash"
 	"github.com/ProtonMail/proton-bridge/v3/internal/usertypes"
 	"github.com/ProtonMail/proton-bridge/v3/pkg/cpc"
 	"github.com/sirupsen/logrus"
@@ -91,7 +92,8 @@ type Service struct {
 	lastHandledEventID string
 	isSyncing          atomic.Bool
 
-	observabilitySender observability.Sender
+	observabilitySender  observability.Sender
+	labelConflictManager *LabelConflictManager
 }
 
 func NewService(
@@ -112,6 +114,7 @@ func NewService(
 	maxSyncMemory uint64,
 	showAllMail bool,
 	observabilitySender observability.Sender,
+	getFeatureFlagValueFn unleash.GetFlagValueFn,
 ) *Service {
 	subscriberName := fmt.Sprintf("imap-%v", identityState.User.ID)
 
@@ -121,7 +124,8 @@ func NewService(
 	})
 	rwIdentity := newRWIdentity(identityState, bridgePassProvider, keyPassProvider)
 
-	syncUpdateApplier := NewSyncUpdateApplier()
+	labelConflictManager := NewLabelConflictManager(serverManager, gluonIDProvider, client, reporter, getFeatureFlagValueFn)
+	syncUpdateApplier := NewSyncUpdateApplier(labelConflictManager)
 	syncMessageBuilder := NewSyncMessageBuilder(rwIdentity)
 	syncReporter := newSyncReporter(identityState.User.ID, eventPublisher, time.Second)
 
@@ -156,7 +160,8 @@ func NewService(
 		syncReporter:       syncReporter,
 		syncConfigPath:     GetSyncConfigPath(syncConfigDir, identityState.User.ID),
 
-		observabilitySender: observabilitySender,
+		observabilitySender:  observabilitySender,
+		labelConflictManager: labelConflictManager,
 	}
 }
 

internal/services/imapservice/service_address_events.go

@@ -165,7 +165,7 @@ func addNewAddressSplitMode(ctx context.Context, s *Service, addrID string) erro
 
 	s.connectors[connector.addrID] = connector
 
-	updates, err := syncLabels(ctx, s.labels.GetLabelMap(), []*Connector{connector})
+	updates, err := syncLabels(ctx, s.labels.GetLabelMap(), []*Connector{connector}, s.labelConflictManager)
 	if err != nil {
 		return fmt.Errorf("failed to create labels updates for new address: %w", err)
 	}

internal/services/imapservice/service_label_events.go

@@ -42,7 +42,10 @@ func (s *Service) HandleLabelEvents(ctx context.Context, events []proton.LabelEv
 				continue
 			}
 
-			updates := onLabelCreated(ctx, s, event)
+			updates, err := onLabelCreated(ctx, s, event)
+			if err != nil {
+				return fmt.Errorf("failed to handle create label event: %w", err)
+			}
 
 			if err := waitOnIMAPUpdates(ctx, updates); err != nil {
 				return err
@@ -74,8 +77,8 @@ func (s *Service) HandleLabelEvents(ctx context.Context, events []proton.LabelEv
 	return nil
 }
 
-func onLabelCreated(ctx context.Context, s *Service, event proton.LabelEvent) []imap.Update {
+func onLabelCreated(ctx context.Context, s *Service, event proton.LabelEvent) ([]imap.Update, error) {
-	updates := make([]imap.Update, 0, len(s.connectors))
+	updates := []imap.Update{}
 
 	s.log.WithFields(logrus.Fields{
 		"labelID": event.ID,
@@ -87,7 +90,17 @@ func onLabelCreated(ctx context.Context, s *Service, event proton.LabelEvent) []
 
 	wr.SetLabel(event.Label.ID, event.Label, "onLabelCreated")
 
+	labelConflictResolver := s.labelConflictManager.NewConflictResolver(maps.Values(s.connectors))
+	conflictUpdatesGenerator, err := labelConflictResolver.ResolveConflict(ctx, event.Label, make(map[string]bool))
+	if err != nil {
+		return updates, err
+	}
+
 	for _, updateCh := range maps.Values(s.connectors) {
+		conflictUpdates := conflictUpdatesGenerator()
+		updateCh.publishUpdate(ctx, conflictUpdates...)
+		updates = append(updates, conflictUpdates...)
+
 		update := newMailboxCreatedUpdate(imap.MailboxID(event.ID), GetMailboxName(event.Label))
 		updateCh.publishUpdate(ctx, update)
 		updates = append(updates, update)
@@ -99,7 +112,7 @@ func onLabelCreated(ctx context.Context, s *Service, event proton.LabelEvent) []
 		Name:    event.Label.Name,
 	})
 
-	return updates
+	return updates, nil
 }
 
 func onLabelUpdated(ctx context.Context, s *Service, event proton.LabelEvent) ([]imap.Update, error) {
@@ -136,8 +149,19 @@ func onLabelUpdated(ctx context.Context, s *Service, event proton.LabelEvent) ([
 		// Update the label in the map.
 		wr.SetLabel(apiLabel.ID, apiLabel, "onLabelUpdatedApiID")
 
+		// Resolve potential conflicts
+		labelConflictResolver := s.labelConflictManager.NewConflictResolver(maps.Values(s.connectors))
+		conflictUpdatesGenerator, err := labelConflictResolver.ResolveConflict(ctx, event.Label, make(map[string]bool))
+		if err != nil {
+			return updates, err
+		}
+
 		// Notify the IMAP clients.
 		for _, updateCh := range maps.Values(s.connectors) {
+			conflictUpdates := conflictUpdatesGenerator()
+			updateCh.publishUpdate(ctx, conflictUpdates...)
+			updates = append(updates, conflictUpdates...)
+
 			update := imap.NewMailboxUpdated(
 				imap.MailboxID(apiLabel.ID),
 				GetMailboxName(apiLabel),

internal/services/imapservice/sync_update_applier.go

@@ -31,8 +31,9 @@ import (
 )
 
 type SyncUpdateApplier struct {
-	requestCh chan updateRequest
+	requestCh            chan updateRequest
-	replyCh   chan updateReply
+	replyCh              chan updateReply
+	labelConflictManager *LabelConflictManager
 }
 
 type updateReply struct {
@@ -42,10 +43,11 @@ type updateReply struct {
 
 type updateRequest = func(ctx context.Context, mode usertypes.AddressMode, connectors map[string]*Connector) ([]imap.Update, error)
 
-func NewSyncUpdateApplier() *SyncUpdateApplier {
+func NewSyncUpdateApplier(labelConflictManager *LabelConflictManager) *SyncUpdateApplier {
 	return &SyncUpdateApplier{
-		requestCh: make(chan updateRequest),
+		requestCh:            make(chan updateRequest),
-		replyCh:   make(chan updateReply),
+		replyCh:              make(chan updateReply),
+		labelConflictManager: labelConflictManager,
 	}
 }
 
@@ -113,7 +115,7 @@ func (s *SyncUpdateApplier) ApplySyncUpdates(ctx context.Context, updates []sync
 
 func (s *SyncUpdateApplier) SyncLabels(ctx context.Context, labels map[string]proton.Label) error {
 	request := func(ctx context.Context, _ usertypes.AddressMode, connectors map[string]*Connector) ([]imap.Update, error) {
-		return syncLabels(ctx, labels, maps.Values(connectors))
+		return syncLabels(ctx, labels, maps.Values(connectors), s.labelConflictManager)
 	}
 
 	updates, err := s.sendRequest(ctx, request)
@@ -128,9 +130,11 @@ func (s *SyncUpdateApplier) SyncLabels(ctx context.Context, labels map[string]pr
 }
 
 // nolint:exhaustive
-func syncLabels(ctx context.Context, labels map[string]proton.Label, connectors []*Connector) ([]imap.Update, error) {
+func syncLabels(ctx context.Context, labels map[string]proton.Label, connectors []*Connector, labelConflictManager *LabelConflictManager) ([]imap.Update, error) {
 	var updates []imap.Update
 
+	labelConflictResolver := labelConflictManager.NewConflictResolver(connectors)
+
 	// Create placeholder Folders/Labels mailboxes with the \Noselect attribute.
 	for _, prefix := range []string{folderPrefix, labelPrefix} {
 		for _, updateCh := range connectors {
@@ -155,7 +159,16 @@ func syncLabels(ctx context.Context, labels map[string]proton.Label, connectors
 			}
 
 		case proton.LabelTypeFolder, proton.LabelTypeLabel:
+			conflictUpdatesGenerator, err := labelConflictResolver.ResolveConflict(ctx, label, make(map[string]bool))
+			if err != nil {
+				return updates, err
+			}
+
 			for _, updateCh := range connectors {
+				conflictUpdates := conflictUpdatesGenerator()
+				updateCh.publishUpdate(ctx, conflictUpdates...)
+				updates = append(updates, conflictUpdates...)
+
 				update := newMailboxCreatedUpdate(imap.MailboxID(labelID), GetMailboxName(label))
 				updateCh.publishUpdate(ctx, update)
 				updates = append(updates, update)

internal/services/imapsmtpserver/service.go

@@ -200,6 +200,10 @@ func (sm *Service) RemoveSMTPAccount(ctx context.Context, service *bridgesmtp.Se
 	return err
 }
 
+func (sm *Service) GetUserMailboxByName(ctx context.Context, addrID string, mailboxName []string) (imap.MailboxData, error) {
+	return sm.imapServer.GetUserMailboxByName(ctx, addrID, mailboxName)
+}
+
 func (sm *Service) run(ctx context.Context, subscription events.Subscription) {
 	eventSub := subscription.Add()
 	defer subscription.Remove(eventSub)

internal/unleash/service.go

@@ -41,6 +41,7 @@ const (
 	IMAPAuthenticateCommandDisabled          = "InboxBridgeImapAuthenticateCommandDisabled"
 	UserRemovalGluonDataCleanupDisabled      = "InboxBridgeUserRemovalGluonDataCleanupDisabled"
 	UpdateUseNewVersionFileStructureDisabled = "InboxBridgeUpdateWithOsFilterDisabled"
+	LabelConflictResolverDisabled            = "InboxBridgeLabelConflictResolverDisabled"
 )
 
 type requestFeaturesFn func(ctx context.Context) (proton.FeatureFlagResult, error)

internal/user/user.go

@@ -282,6 +282,7 @@ func newImpl(
 		user.maxSyncMemory,
 		showAllMail,
 		observabilityService,
+		getFlagValueFn,
 	)
 
 	user.notificationService = notifications.NewService(user.id, user.eventService, user, notificationStore, getFlagValueFn, observabilityService)