diff --git a/app/src/main/java/eu/faircode/email/FragmentMessages.java b/app/src/main/java/eu/faircode/email/FragmentMessages.java
index c11d91903b..4568aef97a 100644
--- a/app/src/main/java/eu/faircode/email/FragmentMessages.java
+++ b/app/src/main/java/eu/faircode/email/FragmentMessages.java
@@ -4991,6 +4991,43 @@ public class FragmentMessages extends FragmentBase implements SharedPreferences.
         }
     }
 
+    private void handleExit() {
+        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getContext());
+        boolean auto_undecrypt = prefs.getBoolean("auto_undecrypt", false);
+        if (auto_undecrypt) {
+            List<Long> ids = new ArrayList<>();
+            for (int i = 0; i < adapter.getItemCount(); i++) {
+                TupleMessageEx message = adapter.getItemAtPosition(i);
+                if (message == null)
+                    continue;
+                if ((EntityMessage.PGP_SIGNENCRYPT.equals(message.ui_encrypt) &&
+                        !EntityMessage.PGP_SIGNENCRYPT.equals(message.encrypt)) ||
+                        (EntityMessage.SMIME_SIGNENCRYPT.equals(message.ui_encrypt) &&
+                                !EntityMessage.SMIME_SIGNENCRYPT.equals(message.encrypt)))
+                    ids.add(message.id);
+            }
+
+            Bundle args = new Bundle();
+            args.putLongArray("ids", Helper.toLongArray(ids));
+
+            new SimpleTask<Void>() {
+                @Override
+                protected Void onExecute(Context context, Bundle args) throws Throwable {
+                    long[] ids = args.getLongArray("ids");
+
+                    for (long id : ids)
+                        lockMessage(id);
+                    return null;
+                }
+
+                @Override
+                protected void onException(Bundle args, Throwable ex) {
+                    Log.unexpectedError(getParentFragmentManager(), ex);
+                }
+            }.execute(this, args, "messages:lock");
+        }
+    }
+
     private void navigate(long id, final boolean left) {
         if (!getLifecycle().getCurrentState().isAtLeast(Lifecycle.State.STARTED))
             return;
@@ -5450,6 +5487,8 @@ public class FragmentMessages extends FragmentBase implements SharedPreferences.
                 return true;
             }
 
+            handleExit();
+
             return false;
         }
 
diff --git a/app/src/main/java/eu/faircode/email/FragmentOptionsEncryption.java b/app/src/main/java/eu/faircode/email/FragmentOptionsEncryption.java
index e0542e8fe6..c4d187f24a 100644
--- a/app/src/main/java/eu/faircode/email/FragmentOptionsEncryption.java
+++ b/app/src/main/java/eu/faircode/email/FragmentOptionsEncryption.java
@@ -72,6 +72,7 @@ public class FragmentOptionsEncryption extends FragmentBase implements SharedPre
     private SwitchCompat swSign;
     private SwitchCompat swEncrypt;
     private SwitchCompat swAutoDecrypt;
+    private SwitchCompat swAutoUndoDecrypt;
 
     private Spinner spOpenPgp;
     private TextView tvOpenPgpStatus;
@@ -90,7 +91,7 @@ public class FragmentOptionsEncryption extends FragmentBase implements SharedPre
     private List<String> openPgpProvider = new ArrayList<>();
 
     private final static String[] RESET_OPTIONS = new String[]{
-            "sign_default", "encrypt_default", "auto_decrypt",
+            "sign_default", "encrypt_default", "auto_decrypt", "auto_undecrypt",
             "openpgp_provider", "autocrypt", "autocrypt_mutual", "encrypt_subject",
             "check_certificate"
     };
@@ -109,6 +110,7 @@ public class FragmentOptionsEncryption extends FragmentBase implements SharedPre
         swSign = view.findViewById(R.id.swSign);
         swEncrypt = view.findViewById(R.id.swEncrypt);
         swAutoDecrypt = view.findViewById(R.id.swAutoDecrypt);
+        swAutoUndoDecrypt = view.findViewById(R.id.swAutoUndoDecrypt);
 
         spOpenPgp = view.findViewById(R.id.spOpenPgp);
         tvOpenPgpStatus = view.findViewById(R.id.tvOpenPgpStatus);
@@ -170,6 +172,13 @@ public class FragmentOptionsEncryption extends FragmentBase implements SharedPre
             }
         });
 
+        swAutoUndoDecrypt.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
+            @Override
+            public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
+                prefs.edit().putBoolean("auto_undecrypt", checked).apply();
+            }
+        });
+
         // PGP
 
         spOpenPgp.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@@ -363,6 +372,7 @@ public class FragmentOptionsEncryption extends FragmentBase implements SharedPre
         swEncrypt.setChecked(prefs.getBoolean("encrypt_default", false));
         swSign.setEnabled(!swEncrypt.isChecked());
         swAutoDecrypt.setChecked(prefs.getBoolean("auto_decrypt", false));
+        swAutoUndoDecrypt.setChecked(prefs.getBoolean("auto_undecrypt", false));
 
         String provider = prefs.getString("openpgp_provider", "org.sufficientlysecure.keychain");
         spOpenPgp.setTag(provider);
diff --git a/app/src/main/res/layout/fragment_options_encryption.xml b/app/src/main/res/layout/fragment_options_encryption.xml
index a15317a684..60f8ea0245 100644
--- a/app/src/main/res/layout/fragment_options_encryption.xml
+++ b/app/src/main/res/layout/fragment_options_encryption.xml
@@ -73,6 +73,17 @@
             app:layout_constraintTop_toBottomOf="@id/swEncrypt"
             app:switchPadding="12dp" />
 
+        <androidx.appcompat.widget.SwitchCompat
+            android:id="@+id/swAutoUndoDecrypt"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="12dp"
+            android:text="@string/title_advanced_auto_undo_decrypt"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@id/swAutoDecrypt"
+            app:switchPadding="12dp" />
+
         <!-- PGP -->
 
         <eu.faircode.email.FixedTextView
@@ -85,7 +96,7 @@
             android:textAppearance="@style/TextAppearance.AppCompat.Large"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/swAutoDecrypt" />
+            app:layout_constraintTop_toBottomOf="@id/swAutoUndoDecrypt" />
 
         <eu.faircode.email.FixedTextView
             android:id="@+id/tvOpenPgp"
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 5dbc3913ac..96ef4fdc83 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -487,6 +487,7 @@
     <string name="title_advanced_sign_default">Sign by default</string>
     <string name="title_advanced_encrypt_default">Encrypt by default</string>
     <string name="title_advanced_auto_decrypt">Automatically decrypt messages</string>
+    <string name="title_advanced_auto_undo_decrypt">Undo decryption on closing conversation</string>
     <string name="title_advanced_openpgp">OpenPGP provider</string>
     <string name="title_advanced_autocrypt">Use Autocrypt</string>
     <string name="title_advanced_autocrypt_mutual">Autocrypt mutual mode</string>