diff --git a/app/src/main/java/com/infomaniak/mail/data/cache/RealmDatabase.kt b/app/src/main/java/com/infomaniak/mail/data/cache/RealmDatabase.kt
index 8ace97abbe..82c7153315 100644
--- a/app/src/main/java/com/infomaniak/mail/data/cache/RealmDatabase.kt
+++ b/app/src/main/java/com/infomaniak/mail/data/cache/RealmDatabase.kt
@@ -161,7 +161,7 @@ object RealmDatabase {
         //region Configurations versions
         const val USER_INFO_SCHEMA_VERSION = 2L
         const val MAILBOX_INFO_SCHEMA_VERSION = 7L
-        const val MAILBOX_CONTENT_SCHEMA_VERSION = 19L
+        const val MAILBOX_CONTENT_SCHEMA_VERSION = 20L
         //endregion
 
         //region Configurations names
diff --git a/app/src/main/java/com/infomaniak/mail/data/cache/RealmMigrations.kt b/app/src/main/java/com/infomaniak/mail/data/cache/RealmMigrations.kt
index cb6dd7c90f..b832cbee58 100644
--- a/app/src/main/java/com/infomaniak/mail/data/cache/RealmMigrations.kt
+++ b/app/src/main/java/com/infomaniak/mail/data/cache/RealmMigrations.kt
@@ -21,6 +21,7 @@ import com.infomaniak.mail.utils.SentryDebug
 import io.realm.kotlin.dynamic.DynamicMutableRealmObject
 import io.realm.kotlin.dynamic.DynamicRealmObject
 import io.realm.kotlin.dynamic.getValue
+import io.realm.kotlin.ext.realmSetOf
 import io.realm.kotlin.migration.AutomaticSchemaMigration
 import io.realm.kotlin.migration.AutomaticSchemaMigration.MigrationContext
 
@@ -38,6 +39,7 @@ val MAILBOX_INFO_MIGRATION = AutomaticSchemaMigration { migrationContext ->
 val MAILBOX_CONTENT_MIGRATION = AutomaticSchemaMigration { migrationContext ->
     SentryDebug.addMigrationBreadcrumb(migrationContext)
     migrationContext.deleteRealmFromFirstMigration()
+    migrationContext.keepThreadsInFolderAfterNineteenthMigration()
 }
 
 // Migrate to version #1
@@ -73,3 +75,20 @@ private fun MigrationContext.keepDefaultValuesAfterSixthMigration() {
         }
     }
 }
+
+/**
+ * Migrate from version #19
+ */
+private fun MigrationContext.keepThreadsInFolderAfterNineteenthMigration() {
+    if (oldRealm.schemaVersion() <= 19L) {
+        enumerate(className = "Folder") { oldObject: DynamicRealmObject, newObject: DynamicMutableRealmObject? ->
+            newObject?.apply {
+                // Backup previous value
+                set(
+                    propertyName = "threads",
+                    value = oldObject.getObjectList(propertyName = "threads").mapTo(realmSetOf(), newRealm::findLatest),
+                )
+            }
+        }
+    }
+}
diff --git a/app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/FolderController.kt b/app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/FolderController.kt
index e5ae656aa1..a29436665e 100644
--- a/app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/FolderController.kt
+++ b/app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/FolderController.kt
@@ -30,7 +30,7 @@ import io.realm.kotlin.MutableRealm
 import io.realm.kotlin.Realm
 import io.realm.kotlin.TypedRealm
 import io.realm.kotlin.ext.query
-import io.realm.kotlin.ext.realmListOf
+import io.realm.kotlin.ext.realmSetOf
 import io.realm.kotlin.notifications.ResultsChange
 import io.realm.kotlin.query.RealmQuery
 import io.realm.kotlin.query.RealmResults
@@ -213,7 +213,7 @@ class FolderController @Inject constructor(
         }
 
         fun deleteSearchFolderData(realm: MutableRealm) = with(getOrCreateSearchFolder(realm)) {
-            threads = realmListOf()
+            threads = realmSetOf()
         }
         //endregion
     }
diff --git a/app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/ThreadController.kt b/app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/ThreadController.kt
index e25d97dcb2..804cf7ac19 100644
--- a/app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/ThreadController.kt
+++ b/app/src/main/java/com/infomaniak/mail/data/cache/mailboxContent/ThreadController.kt
@@ -40,7 +40,7 @@ import io.realm.kotlin.UpdatePolicy
 import io.realm.kotlin.ext.isManaged
 import io.realm.kotlin.ext.query
 import io.realm.kotlin.ext.realmListOf
-import io.realm.kotlin.ext.toRealmList
+import io.realm.kotlin.ext.toRealmSet
 import io.realm.kotlin.notifications.ResultsChange
 import io.realm.kotlin.notifications.SingleQueryChange
 import io.realm.kotlin.query.*
@@ -169,7 +169,7 @@ class ThreadController @Inject constructor(
     suspend fun saveThreads(searchMessages: List<Message>) {
         mailboxContentRealm().write {
             FolderController.getOrCreateSearchFolder(realm = this).apply {
-                threads = searchMessages.convertToSearchThreads().toRealmList()
+                threads = searchMessages.convertToSearchThreads().toRealmSet()
             }
         }
     }
diff --git a/app/src/main/java/com/infomaniak/mail/data/models/Folder.kt b/app/src/main/java/com/infomaniak/mail/data/models/Folder.kt
index 76514c37d7..94d0e74091 100644
--- a/app/src/main/java/com/infomaniak/mail/data/models/Folder.kt
+++ b/app/src/main/java/com/infomaniak/mail/data/models/Folder.kt
@@ -34,10 +34,12 @@ import com.infomaniak.mail.utils.Utils
 import io.realm.kotlin.TypedRealm
 import io.realm.kotlin.ext.backlinks
 import io.realm.kotlin.ext.realmListOf
+import io.realm.kotlin.ext.realmSetOf
 import io.realm.kotlin.serializers.RealmListKSerializer
 import io.realm.kotlin.types.RealmInstant
 import io.realm.kotlin.types.RealmList
 import io.realm.kotlin.types.RealmObject
+import io.realm.kotlin.types.RealmSet
 import io.realm.kotlin.types.annotations.PrimaryKey
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
@@ -70,7 +72,7 @@ class Folder : RealmObject, Cloneable {
     @Transient
     var unreadCountLocal: Int = 0
     @Transient
-    var threads = realmListOf<Thread>()
+    var threads = realmSetOf<Thread>()
 
     /**
      * List of old Messages UIDs of this Folder that we need to fetch.
@@ -119,7 +121,7 @@ class Folder : RealmObject, Cloneable {
         lastUpdatedAt: RealmInstant?,
         cursor: String?,
         unreadCount: Int,
-        threads: RealmList<Thread>,
+        threads: RealmSet<Thread>,
         oldMessagesUidsToFetch: RealmList<Int>,
         newMessagesUidsToFetch: RealmList<Int>,
         remainingOldMessagesToFetch: Int,
diff --git a/app/src/main/java/com/infomaniak/mail/data/models/thread/Thread.kt b/app/src/main/java/com/infomaniak/mail/data/models/thread/Thread.kt
index 6c1be59b4a..7b740c145e 100644
--- a/app/src/main/java/com/infomaniak/mail/data/models/thread/Thread.kt
+++ b/app/src/main/java/com/infomaniak/mail/data/models/thread/Thread.kt
@@ -97,6 +97,7 @@ class Thread : RealmObject {
     var isLocallyMovedOut: Boolean = false
     //endregion
 
+    // TODO: Remove this `runCatching / getOrElse` when the issue is fixed
     private val _folders by backlinks(Folder::threads)
     val folder
         get() = runCatching {