diff --git a/app/k9mail/src/main/java/com/fsck/k9/external/MessageInfoHolder.java b/app/k9mail/src/main/java/com/fsck/k9/external/MessageInfoHolder.java
index a1142f9bd..16f7bc573 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/external/MessageInfoHolder.java
+++ b/app/k9mail/src/main/java/com/fsck/k9/external/MessageInfoHolder.java
@@ -1,5 +1,6 @@
 package com.fsck.k9.external;
 
+
 import java.util.Date;
 
 import android.content.Context;
@@ -7,13 +8,13 @@ import android.text.SpannableStringBuilder;
 
 import com.fsck.k9.Account;
 import com.fsck.k9.K9;
-import com.fsck.k9.R;
 import com.fsck.k9.helper.Contacts;
 import com.fsck.k9.helper.MessageHelper;
 import com.fsck.k9.mail.Address;
 import com.fsck.k9.mail.Flag;
 import com.fsck.k9.mail.Message.RecipientType;
 import com.fsck.k9.mailstore.LocalMessage;
+import com.fsck.k9.ui.R;
 
 class MessageInfoHolder {
     public Date compareDate;
diff --git a/app/k9mail/src/main/java/com/fsck/k9/notification/K9NotificationResourceProvider.kt b/app/k9mail/src/main/java/com/fsck/k9/notification/K9NotificationResourceProvider.kt
index 033030e8d..aac16b241 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/notification/K9NotificationResourceProvider.kt
+++ b/app/k9mail/src/main/java/com/fsck/k9/notification/K9NotificationResourceProvider.kt
@@ -1,7 +1,7 @@
 package com.fsck.k9.notification
 
 import android.content.Context
-import com.fsck.k9.R
+import com.fsck.k9.ui.R
 
 class K9NotificationResourceProvider(private val context: Context) : NotificationResourceProvider {
     override val iconWarning: Int = R.drawable.notification_icon_warning
diff --git a/app/k9mail/src/main/java/com/fsck/k9/resources/K9AutocryptStringProvider.kt b/app/k9mail/src/main/java/com/fsck/k9/resources/K9AutocryptStringProvider.kt
index a24958e15..411ad4eab 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/resources/K9AutocryptStringProvider.kt
+++ b/app/k9mail/src/main/java/com/fsck/k9/resources/K9AutocryptStringProvider.kt
@@ -1,8 +1,8 @@
 package com.fsck.k9.resources
 
 import android.content.Context
-import com.fsck.k9.R
 import com.fsck.k9.autocrypt.AutocryptStringProvider
+import com.fsck.k9.ui.R
 
 class K9AutocryptStringProvider(private val context: Context) : AutocryptStringProvider {
     override fun transferMessageSubject(): String = context.getString(R.string.ac_transfer_msg_subject)
diff --git a/app/k9mail/src/main/java/com/fsck/k9/resources/K9CoreResourceProvider.kt b/app/k9mail/src/main/java/com/fsck/k9/resources/K9CoreResourceProvider.kt
index 270736c3e..d2ec95094 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/resources/K9CoreResourceProvider.kt
+++ b/app/k9mail/src/main/java/com/fsck/k9/resources/K9CoreResourceProvider.kt
@@ -2,8 +2,8 @@ package com.fsck.k9.resources
 
 import android.content.Context
 import com.fsck.k9.CoreResourceProvider
-import com.fsck.k9.R
 import com.fsck.k9.notification.PushNotificationState
+import com.fsck.k9.ui.R
 
 class K9CoreResourceProvider(private val context: Context) : CoreResourceProvider {
     override fun defaultSignature(): String = context.getString(R.string.default_signature)
diff --git a/app/k9mail/src/main/java/com/fsck/k9/widget/list/MessageListRemoteViewFactory.java b/app/k9mail/src/main/java/com/fsck/k9/widget/list/MessageListRemoteViewFactory.java
index 3d9af2ea2..5ebc41157 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/widget/list/MessageListRemoteViewFactory.java
+++ b/app/k9mail/src/main/java/com/fsck/k9/widget/list/MessageListRemoteViewFactory.java
@@ -147,7 +147,7 @@ public class MessageListRemoteViewFactory implements RemoteViewsService.RemoteVi
     @Override
     public RemoteViews getLoadingView() {
         RemoteViews loadingView = new RemoteViews(context.getPackageName(), R.layout.message_list_widget_loading);
-        loadingView.setTextViewText(R.id.loadingText, context.getString(R.string.mail_list_widget_loading));
+        loadingView.setTextViewText(R.id.loadingText, context.getString(com.fsck.k9.ui.R.string.mail_list_widget_loading));
         loadingView.setViewVisibility(R.id.loadingText, View.VISIBLE);
         return loadingView;
     }
diff --git a/app/k9mail/src/main/java/com/fsck/k9/widget/list/MessageListWidgetProvider.java b/app/k9mail/src/main/java/com/fsck/k9/widget/list/MessageListWidgetProvider.java
index f6c799b7e..c7a9ac007 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/widget/list/MessageListWidgetProvider.java
+++ b/app/k9mail/src/main/java/com/fsck/k9/widget/list/MessageListWidgetProvider.java
@@ -46,7 +46,7 @@ public class MessageListWidgetProvider extends AppWidgetProvider {
     private void updateAppWidget(Context context, AppWidgetManager appWidgetManager, int appWidgetId) {
         RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.message_list_widget_layout);
 
-        views.setTextViewText(R.id.folder, context.getString(R.string.integrated_inbox_title));
+        views.setTextViewText(R.id.folder, context.getString(com.fsck.k9.ui.R.string.integrated_inbox_title));
 
         Intent intent = new Intent(context, MessageListWidgetService.class);
         intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetId);
diff --git a/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetConfigurationActivity.kt b/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetConfigurationActivity.kt
index d3a617f9d..fa1662b0d 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetConfigurationActivity.kt
+++ b/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetConfigurationActivity.kt
@@ -6,6 +6,7 @@ import com.fsck.k9.R
 import com.fsck.k9.ui.base.K9Activity
 import com.fsck.k9.ui.fragmentTransaction
 import timber.log.Timber
+import com.fsck.k9.ui.R as UiR
 
 /**
  * Activity to select an account for the unread widget.
@@ -15,7 +16,7 @@ class UnreadWidgetConfigurationActivity : K9Activity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setLayout(R.layout.activity_unread_widget_configuration)
-        setTitle(R.string.unread_widget_select_account)
+        setTitle(UiR.string.unread_widget_select_account)
 
         var appWidgetId = AppWidgetManager.INVALID_APPWIDGET_ID
         val extras = intent.extras
diff --git a/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetConfigurationFragment.kt b/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetConfigurationFragment.kt
index 92a3a7564..5c9a19f73 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetConfigurationFragment.kt
+++ b/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetConfigurationFragment.kt
@@ -18,6 +18,7 @@ import com.fsck.k9.search.SearchAccount
 import com.fsck.k9.ui.choosefolder.ChooseFolderActivity
 import com.takisoft.preferencex.PreferenceFragmentCompat
 import org.koin.android.ext.android.inject
+import com.fsck.k9.ui.R as UiR
 
 class UnreadWidgetConfigurationFragment : PreferenceFragmentCompat() {
     private val preferences: Preferences by inject()
@@ -48,7 +49,7 @@ class UnreadWidgetConfigurationFragment : PreferenceFragmentCompat() {
 
         unreadFolderEnabled = findPreference(PREFERENCE_UNREAD_FOLDER_ENABLED)!!
         unreadFolderEnabled.onPreferenceChangeListener = Preference.OnPreferenceChangeListener { _, _ ->
-            unreadFolder.summary = getString(R.string.unread_widget_folder_summary)
+            unreadFolder.summary = getString(UiR.string.unread_widget_folder_summary)
             selectedFolderId = null
             selectedFolderDisplayName = null
             true
@@ -116,7 +117,7 @@ class UnreadWidgetConfigurationFragment : PreferenceFragmentCompat() {
         selectedAccountUuid = accountUuid
         selectedFolderId = null
         selectedFolderDisplayName = null
-        unreadFolder.summary = getString(R.string.unread_widget_folder_summary)
+        unreadFolder.summary = getString(UiR.string.unread_widget_folder_summary)
         if (SearchAccount.UNIFIED_INBOX == selectedAccountUuid) {
             handleSearchAccount()
         } else {
@@ -126,7 +127,7 @@ class UnreadWidgetConfigurationFragment : PreferenceFragmentCompat() {
 
     private fun handleSearchAccount() {
         if (SearchAccount.UNIFIED_INBOX == selectedAccountUuid) {
-            unreadAccount.setSummary(R.string.unread_widget_unified_inbox_account_summary)
+            unreadAccount.setSummary(UiR.string.unread_widget_unified_inbox_account_summary)
         }
         unreadFolderEnabled.isEnabled = false
         unreadFolderEnabled.isChecked = false
@@ -168,10 +169,10 @@ class UnreadWidgetConfigurationFragment : PreferenceFragmentCompat() {
 
     private fun validateWidget(): Boolean {
         if (selectedAccountUuid == null) {
-            Toast.makeText(requireContext(), R.string.unread_widget_account_not_selected, Toast.LENGTH_LONG).show()
+            Toast.makeText(requireContext(), UiR.string.unread_widget_account_not_selected, Toast.LENGTH_LONG).show()
             return false
         } else if (unreadFolderEnabled.isChecked && selectedFolderId == null) {
-            Toast.makeText(requireContext(), R.string.unread_widget_folder_not_selected, Toast.LENGTH_LONG).show()
+            Toast.makeText(requireContext(), UiR.string.unread_widget_folder_not_selected, Toast.LENGTH_LONG).show()
             return false
         }
         return true
diff --git a/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetDataProvider.kt b/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetDataProvider.kt
index 4766a43be..78df3d9cf 100644
--- a/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetDataProvider.kt
+++ b/app/k9mail/src/main/java/com/fsck/k9/widget/unread/UnreadWidgetDataProvider.kt
@@ -4,7 +4,6 @@ import android.content.Context
 import android.content.Intent
 import com.fsck.k9.Account
 import com.fsck.k9.Preferences
-import com.fsck.k9.R
 import com.fsck.k9.activity.MessageList
 import com.fsck.k9.controller.MessagingController
 import com.fsck.k9.mailstore.FolderRepository
@@ -13,6 +12,7 @@ import com.fsck.k9.search.SearchAccount
 import com.fsck.k9.ui.folders.FolderNameFormatterFactory
 import com.fsck.k9.ui.messagelist.DefaultFolderProvider
 import timber.log.Timber
+import com.fsck.k9.ui.R as UiR
 
 class UnreadWidgetDataProvider(
     private val context: Context,
@@ -68,7 +68,7 @@ class UnreadWidgetDataProvider(
 
         val accountName = account.displayName
         val folderDisplayName = getFolderDisplayName(account, folderId)
-        val title = context.getString(R.string.unread_widget_title, accountName, folderDisplayName)
+        val title = context.getString(UiR.string.unread_widget_title, accountName, folderDisplayName)
 
         val unreadCount = messagingController.getFolderUnreadMessageCount(account, folderId)
 
diff --git a/app/ui/legacy/src/main/java/com/fsck/k9/account/AccountCreator.kt b/app/ui/legacy/src/main/java/com/fsck/k9/account/AccountCreator.kt
index e3f49d16a..db6c0824d 100644
--- a/app/ui/legacy/src/main/java/com/fsck/k9/account/AccountCreator.kt
+++ b/app/ui/legacy/src/main/java/com/fsck/k9/account/AccountCreator.kt
@@ -3,9 +3,9 @@ package com.fsck.k9.account
 import android.content.res.Resources
 import com.fsck.k9.Account.DeletePolicy
 import com.fsck.k9.Preferences
+import com.fsck.k9.core.R
 import com.fsck.k9.mail.ConnectionSecurity
 import com.fsck.k9.preferences.Protocols
-import com.fsck.k9.ui.R
 import com.fsck.k9.ui.helper.MaterialColors
 
 /**
diff --git a/app/ui/legacy/src/main/java/com/fsck/k9/ui/K9Drawer.kt b/app/ui/legacy/src/main/java/com/fsck/k9/ui/K9Drawer.kt
index 7a8e4feaa..33ea62825 100644
--- a/app/ui/legacy/src/main/java/com/fsck/k9/ui/K9Drawer.kt
+++ b/app/ui/legacy/src/main/java/com/fsck/k9/ui/K9Drawer.kt
@@ -56,6 +56,8 @@ import org.koin.androidx.viewmodel.ext.android.viewModel
 import org.koin.core.component.KoinComponent
 import org.koin.core.component.inject
 import org.koin.core.parameter.parametersOf
+import com.fsck.k9.core.R as CoreR
+import com.mikepenz.materialdrawer.R as MaterialDrawerR
 
 private const val UNREAD_SYMBOL = "\u2B24"
 private const val STARRED_SYMBOL = "\u2605"
@@ -466,8 +468,8 @@ class K9Drawer(private val parent: MessageList, savedInstanceState: Bundle?) : K
     }
 
     private fun getDarkThemeAccentColor(color: Int): Int {
-        val lightColors = resources.getIntArray(R.array.account_colors)
-        val darkColors = resources.getIntArray(R.array.drawer_account_accent_color_dark_theme)
+        val lightColors = resources.getIntArray(CoreR.array.account_colors)
+        val darkColors = resources.getIntArray(CoreR.array.drawer_account_accent_color_dark_theme)
         val index = lightColors.indexOf(color)
         return if (index == -1) color else darkColors[index]
     }
@@ -537,11 +539,11 @@ class K9Drawer(private val parent: MessageList, savedInstanceState: Bundle?) : K
 private fun Context.obtainDrawerTextColor(): Int {
     val styledAttributes = obtainStyledAttributes(
         null,
-        R.styleable.MaterialDrawerSliderView,
-        R.attr.materialDrawerStyle,
-        R.style.Widget_MaterialDrawerStyle
+        MaterialDrawerR.styleable.MaterialDrawerSliderView,
+        MaterialDrawerR.attr.materialDrawerStyle,
+        MaterialDrawerR.style.Widget_MaterialDrawerStyle
     )
-    val textColor = styledAttributes.getColor(R.styleable.MaterialDrawerSliderView_materialDrawerPrimaryText, 0)
+    val textColor = styledAttributes.getColor(MaterialDrawerR.styleable.MaterialDrawerSliderView_materialDrawerPrimaryText, 0)
     styledAttributes.recycle()
 
     return textColor
diff --git a/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/account/OpenPgpAppSelectDialog.java b/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/account/OpenPgpAppSelectDialog.java
index 18af4fcf6..512f385dd 100644
--- a/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/account/OpenPgpAppSelectDialog.java
+++ b/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/account/OpenPgpAppSelectDialog.java
@@ -110,8 +110,8 @@ public class OpenPgpAppSelectDialog extends K9Activity {
             Context context = getActivity();
 
             OpenPgpProviderEntry noneEntry = new OpenPgpProviderEntry(null,
-                    context.getString(R.string.openpgp_list_preference_none),
-                    getResources().getDrawable(R.drawable.ic_action_cancel_launchersize_light));
+                    context.getString(org.openintents.openpgp.R.string.openpgp_list_preference_none),
+                    getResources().getDrawable(org.openintents.openpgp.R.drawable.ic_action_cancel_launchersize_light));
             openPgpProviderList.add(noneEntry);
 
             // search for OpenPGP providers...
@@ -144,8 +144,9 @@ public class OpenPgpAppSelectDialog extends K9Activity {
                     Drawable icon = resolveInfo.activityInfo.loadIcon(context.getPackageManager());
                     String marketName = String.valueOf(resolveInfo.activityInfo.applicationInfo
                             .loadLabel(context.getPackageManager()));
-                    String simpleName = String.format(context.getString(R.string
-                            .openpgp_install_openkeychain_via), marketName);
+                    String simpleName = String.format(
+                            context.getString(org.openintents.openpgp.R.string.openpgp_install_openkeychain_via),
+                            marketName);
                     openPgpProviderList.add(new OpenPgpProviderEntry(OPENKEYCHAIN_PACKAGE, simpleName,
                             icon, marketIntent));
                 }
diff --git a/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/general/GeneralSettingsFragment.kt b/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/general/GeneralSettingsFragment.kt
index f8d31ccab..bf27905f4 100644
--- a/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/general/GeneralSettingsFragment.kt
+++ b/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/general/GeneralSettingsFragment.kt
@@ -14,6 +14,7 @@ import com.google.android.material.snackbar.Snackbar
 import com.takisoft.preferencex.PreferenceFragmentCompat
 import org.koin.android.ext.android.inject
 import org.koin.androidx.viewmodel.ext.android.viewModel
+import com.fsck.k9.core.R as CoreR
 
 class GeneralSettingsFragment : PreferenceFragmentCompat() {
     private val viewModel: GeneralSettingsViewModel by viewModel()
@@ -74,7 +75,7 @@ class GeneralSettingsFragment : PreferenceFragmentCompat() {
         (findPreference(PREFERENCE_THEME) as? ListPreference)?.apply {
             if (Build.VERSION.SDK_INT < 28) {
                 setEntries(R.array.theme_entries_legacy)
-                setEntryValues(R.array.theme_values_legacy)
+                setEntryValues(CoreR.array.theme_values_legacy)
             }
         }
     }
diff --git a/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/general/LanguagePreference.kt b/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/general/LanguagePreference.kt
index f83487f81..8884c2f73 100644
--- a/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/general/LanguagePreference.kt
+++ b/app/ui/legacy/src/main/java/com/fsck/k9/ui/settings/general/LanguagePreference.kt
@@ -5,7 +5,7 @@ import android.content.Context
 import android.util.AttributeSet
 import androidx.core.content.res.TypedArrayUtils
 import androidx.preference.ListPreference
-import com.fsck.k9.ui.R
+import com.fsck.k9.core.R
 
 class LanguagePreference
 @JvmOverloads
diff --git a/app/ui/legacy/src/test/java/com/fsck/k9/ui/K9DrawerTest.kt b/app/ui/legacy/src/test/java/com/fsck/k9/ui/K9DrawerTest.kt
index 48c04348c..7db67cbf5 100644
--- a/app/ui/legacy/src/test/java/com/fsck/k9/ui/K9DrawerTest.kt
+++ b/app/ui/legacy/src/test/java/com/fsck/k9/ui/K9DrawerTest.kt
@@ -1,6 +1,7 @@
 package com.fsck.k9.ui
 
 import com.fsck.k9.RobolectricTest
+import com.fsck.k9.core.R
 import org.junit.Assert.assertEquals
 import org.junit.Test
 import org.robolectric.RuntimeEnvironment
diff --git a/gradle.properties b/gradle.properties
index 3628962fa..2d5e8441c 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -2,3 +2,4 @@ android.useAndroidX=true
 android.enableJetifier=false
 org.gradle.jvmargs=-Xmx1400m
 org.gradle.parallel=true
+android.nonTransitiveRClass=true