Added Gmail threading hint

app/src/main/res/layout/fragment_options_synchronize.xml

@@ -420,6 +420,18 @@
             app:layout_constraintTop_toBottomOf="@id/tvSyncKeptHint"
             app:switchPadding="12dp" />
 
+        <eu.faircode.email.FixedTextView
+            android:id="@+id/tvGmailThreadHint"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_marginEnd="48dp"
+            android:text="@string/title_advanced_gmail_thread_hint"
+            android:textAppearance="@style/TextAppearance.AppCompat.Small"
+            android:textStyle="italic"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@id/swGmailThread" />
+
         <androidx.appcompat.widget.SwitchCompat
             android:id="@+id/swSyncFolders"
             android:layout_width="0dp"
@@ -429,7 +441,7 @@
             android:text="@string/title_advanced_sync_folders"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/swGmailThread"
+            app:layout_constraintTop_toBottomOf="@id/tvGmailThreadHint"
             app:switchPadding="12dp" />
 
         <eu.faircode.email.FixedTextView

app/src/main/res/values/strings.xml

@@ -548,6 +548,7 @@
     <string name="title_advanced_unseen_hint">Some providers don\'t support this properly, which may cause synchronizing none or all messages</string>
     <string name="title_advanced_deleted_unseen">When disabled, unread messages are kept on the device forever</string>
     <string name="title_advanced_sync_kept_hint">This will transfer extra data and consume extra battery power, especially if a lot of messages are stored on the device</string>
+    <string name="title_advanced_gmail_thread_hint">This only applies to newly received messages and can break existing groups</string>
     <string name="title_advanced_sync_folders_hint">Disabling this will reduce data and battery usage somewhat, but will disable updating the list of folders too</string>
     <string name="title_advanced_lookup_mx_hint">This will check if DNS MX records exist</string>
     <string name="title_advanced_sync_delay_hint">This will slow down synchronizing messages</string>