diff --git a/backend/go.mod b/backend/go.mod
index 1f9a62d5..9835b166 100644
--- a/backend/go.mod
+++ b/backend/go.mod
@@ -41,6 +41,7 @@ require (
 	github.com/quic-go/quic-go v0.63.0
 	github.com/spf13/cobra v1.10.2
 	github.com/stretchr/testify v1.12.1
+	github.com/vmihailenco/msgpack/v5 v5.4.1
 	github.com/zitadel/exifremove v0.1.0
 	go.opentelemetry.io/contrib/bridges/otelslog v0.21.0
 	go.opentelemetry.io/contrib/exporters/autoexport v0.72.0
@@ -178,7 +179,6 @@ require (
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.3.2 // indirect
 	github.com/valyala/fastjson v1.6.10 // indirect
-	github.com/vmihailenco/msgpack/v5 v5.4.1 // indirect
 	github.com/vmihailenco/tagparser/v2 v2.0.0 // indirect
 	github.com/x448/float16 v0.8.4 // indirect
 	go.mongodb.org/mongo-driver/v2 v2.9.1 // indirect
diff --git a/backend/internal/appconfig/legacy.go b/backend/internal/appconfig/legacy.go
index a6d45059..65d34be6 100644
--- a/backend/internal/appconfig/legacy.go
+++ b/backend/internal/appconfig/legacy.go
@@ -1,16 +1,17 @@
 package appconfig
 
-import "encoding/json"
+import "github.com/vmihailenco/msgpack/v5"
 
-// UnmarshalJSON preserves settings stored in actor state before boolean toggles were replaced by modes
-func (m *AppConfigModel) UnmarshalJSON(data []byte) error {
+// DecodeMsgpack preserves settings stored in actor state before boolean toggles were replaced by modes
+// Francis stores actor state as MessagePack keyed by Go field name, so the legacy keys are the old field names
+func (m *AppConfigModel) DecodeMsgpack(dec *msgpack.Decoder) error {
 	type config AppConfigModel
 	value := struct {
 		*config
-		LegacyNotificationEnabled      AppConfigValue `json:"emailLoginNotificationEnabled"`
-		LegacyEmailVerificationEnabled AppConfigValue `json:"emailVerificationEnabled"`
+		LegacyNotificationEnabled      AppConfigValue `msgpack:"EmailLoginNotificationEnabled"`
+		LegacyEmailVerificationEnabled AppConfigValue `msgpack:"EmailVerificationEnabled"`
 	}{config: (*config)(m)}
-	if err := json.Unmarshal(data, &value); err != nil {
+	if err := dec.Decode(&value); err != nil {
 		return err
 	}
 	if m.EmailLoginNotificationMode == "" && value.LegacyNotificationEnabled != "" {
diff --git a/backend/internal/appconfig/model_test.go b/backend/internal/appconfig/model_test.go
index d766773e..729c6aa2 100644
--- a/backend/internal/appconfig/model_test.go
+++ b/backend/internal/appconfig/model_test.go
@@ -1,7 +1,6 @@
 package appconfig
 
 import (
-	"encoding/json"
 	"errors"
 	"reflect"
 	"strings"
@@ -9,6 +8,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"github.com/vmihailenco/msgpack/v5"
 
 	"github.com/pocket-id/pocket-id/backend/internal/dto"
 )
@@ -302,26 +302,47 @@ func TestAppConfigModel_Update(t *testing.T) {
 	})
 }
 
-func TestAppConfigModel_UnmarshalJSON(t *testing.T) {
-	t.Run("maps the legacy email verification toggle to a mode", func(t *testing.T) {
-		tests := map[string]AppConfigValue{
-			"true":  EmailVerificationOptional,
-			"false": EmailVerificationDisabled,
+func TestAppConfigModel_DecodeMsgpack(t *testing.T) {
+	t.Run("maps the legacy toggles to modes", func(t *testing.T) {
+		tests := map[string]struct {
+			notification      AppConfigValue
+			emailVerification AppConfigValue
+		}{
+			"true":  {LoginNotificationBrowserRecognition, EmailVerificationOptional},
+			"false": {LoginNotificationDisabled, EmailVerificationDisabled},
 		}
 		for enabled, expected := range tests {
-			var m AppConfigModel
-			err := json.Unmarshal([]byte(`{"emailVerificationEnabled":"`+enabled+`"}`), &m)
+			data, err := msgpack.Marshal(map[string]string{
+				"AppName":                       "Legacy App",
+				"EmailLoginNotificationEnabled": enabled,
+				"EmailVerificationEnabled":      enabled,
+			})
 			require.NoError(t, err)
 
-			assert.Equal(t, expected, m.EmailVerification)
+			var m AppConfigModel
+			err = msgpack.Unmarshal(data, &m)
+			require.NoError(t, err)
+
+			assert.Equal(t, AppConfigValue("Legacy App"), m.AppName)
+			assert.Equal(t, expected.notification, m.EmailLoginNotificationMode)
+			assert.Equal(t, expected.emailVerification, m.EmailVerification)
 		}
 	})
 
-	t.Run("an explicit email verification mode wins over the legacy toggle", func(t *testing.T) {
-		var m AppConfigModel
-		err := json.Unmarshal([]byte(`{"emailVerification":"required","emailVerificationEnabled":"false"}`), &m)
+	t.Run("stored modes win over the legacy toggles", func(t *testing.T) {
+		data, err := msgpack.Marshal(map[string]string{
+			"EmailLoginNotificationMode":    LoginNotificationAlways,
+			"EmailLoginNotificationEnabled": "false",
+			"EmailVerification":             EmailVerificationRequired,
+			"EmailVerificationEnabled":      "false",
+		})
 		require.NoError(t, err)
 
+		var m AppConfigModel
+		err = msgpack.Unmarshal(data, &m)
+		require.NoError(t, err)
+
+		assert.Equal(t, AppConfigValue(LoginNotificationAlways), m.EmailLoginNotificationMode)
 		assert.Equal(t, AppConfigValue(EmailVerificationRequired), m.EmailVerification)
 	})
 }