diff --git a/app/src/main/java/eu/faircode/email/Core.java b/app/src/main/java/eu/faircode/email/Core.java
index 1b72e1db55..cebcf52daa 100644
--- a/app/src/main/java/eu/faircode/email/Core.java
+++ b/app/src/main/java/eu/faircode/email/Core.java
@@ -2144,6 +2144,32 @@ class Core {
                     message.warning = Log.formatThrowable(ex, false);
                 }
 
+            boolean check_reply = prefs.getBoolean("check_reply", false);
+            if (check_reply &&
+                    message.from != null && message.from.length > 0 &&
+                    message.reply != null && message.reply.length > 0) {
+                for (Address reply : message.reply) {
+                    String r = ((InternetAddress) reply).getAddress();
+                    int rat = (r == null ? -1 : r.indexOf('@'));
+                    if (rat > 0) {
+                        String rdomain = r.substring(rat + 1);
+                        for (Address from : message.from) {
+                            String f = ((InternetAddress) from).getAddress();
+                            int fat = (f == null ? -1 : f.indexOf('@'));
+                            if (fat > 0) {
+                                String fdomain = f.substring(fat + 1);
+                                if (!rdomain.equalsIgnoreCase(fdomain)) {
+                                    if (message.warning == null)
+                                        message.warning = context.getString(R.string.title_reply_domain, fdomain, rdomain);
+                                    else
+                                        message.warning += ", " + context.getString(R.string.title_reply_domain, fdomain, rdomain);
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
             if (message.total != null && message.total == 0)
                 reportEmptyMessage(context, account, istore);
 
diff --git a/app/src/main/java/eu/faircode/email/FragmentOptionsSynchronize.java b/app/src/main/java/eu/faircode/email/FragmentOptionsSynchronize.java
index a15f643f36..6266e9b381 100644
--- a/app/src/main/java/eu/faircode/email/FragmentOptionsSynchronize.java
+++ b/app/src/main/java/eu/faircode/email/FragmentOptionsSynchronize.java
@@ -67,10 +67,12 @@ public class FragmentOptionsSynchronize extends FragmentBase implements SharedPr
     private TextView tvSubscriptionPro;
     private SwitchCompat swSubscribedOnly;
     private SwitchCompat swCheckMx;
+    private SwitchCompat swCheckReply;
 
     private final static String[] RESET_OPTIONS = new String[]{
             "enabled", "poll_interval", "schedule", "schedule_start", "schedule_end",
-            "sync_unseen", "sync_flagged", "delete_unseen", "sync_kept", "sync_folders", "subscriptions", "subscribed_only", "check_mx"
+            "sync_unseen", "sync_flagged", "delete_unseen", "sync_kept", "sync_folders", "subscriptions", "subscribed_only",
+            "check_mx", "check_reply"
     };
 
     @Override
@@ -107,6 +109,7 @@ public class FragmentOptionsSynchronize extends FragmentBase implements SharedPr
         tvSubscriptionPro = view.findViewById(R.id.tvSubscriptionPro);
         swSubscribedOnly = view.findViewById(R.id.swSubscribedOnly);
         swCheckMx = view.findViewById(R.id.swCheckMx);
+        swCheckReply = view.findViewById(R.id.swCheckReply);
 
         setOptions();
 
@@ -253,6 +256,13 @@ public class FragmentOptionsSynchronize extends FragmentBase implements SharedPr
             }
         });
 
+        swCheckReply.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
+            @Override
+            public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
+                prefs.edit().putBoolean("check_reply", checked).apply();
+            }
+        });
+
         PreferenceManager.getDefaultSharedPreferences(getContext()).registerOnSharedPreferenceChangeListener(this);
 
         return view;
@@ -327,6 +337,7 @@ public class FragmentOptionsSynchronize extends FragmentBase implements SharedPr
         swSubscriptions.setEnabled(pro);
         swSubscribedOnly.setChecked(prefs.getBoolean("subscribed_only", false));
         swCheckMx.setChecked(prefs.getBoolean("check_mx", false));
+        swCheckReply.setChecked(prefs.getBoolean("check_reply", false));
     }
 
     private String formatHour(Context context, int minutes) {
diff --git a/app/src/main/res/layout/fragment_options_send.xml b/app/src/main/res/layout/fragment_options_send.xml
index 014dcd152c..6bb84a7c0c 100644
--- a/app/src/main/res/layout/fragment_options_send.xml
+++ b/app/src/main/res/layout/fragment_options_send.xml
@@ -206,7 +206,7 @@
             app:switchPadding="12dp" />
 
         <TextView
-            android:id="@+id/tvLookupMxHint"
+            android:id="@+id/tvCheckMxHint"
             android:layout_width="0dp"
             android:layout_height="wrap_content"
             android:layout_marginEnd="48dp"
@@ -228,7 +228,7 @@
             android:textColor="?android:attr/textColorPrimary"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/tvLookupMxHint" />
+            app:layout_constraintTop_toBottomOf="@id/tvCheckMxHint" />
 
         <Spinner
             android:id="@+id/spSendDelayed"
diff --git a/app/src/main/res/layout/fragment_options_synchronize.xml b/app/src/main/res/layout/fragment_options_synchronize.xml
index 8a811289dd..d9aede9aaf 100644
--- a/app/src/main/res/layout/fragment_options_synchronize.xml
+++ b/app/src/main/res/layout/fragment_options_synchronize.xml
@@ -373,7 +373,7 @@
             app:switchPadding="12dp" />
 
         <TextView
-            android:id="@+id/tvLookupMxHint"
+            android:id="@+id/tvCheckMxHint"
             android:layout_width="0dp"
             android:layout_height="wrap_content"
             android:layout_marginEnd="48dp"
@@ -395,6 +395,29 @@
             android:textStyle="italic"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/tvLookupMxHint" />
+            app:layout_constraintTop_toBottomOf="@id/tvCheckMxHint" />
+
+        <androidx.appcompat.widget.SwitchCompat
+            android:id="@+id/swCheckReply"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="12dp"
+            android:text="@string/title_advanced_check_reply"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@id/tvDelayHint"
+            app:switchPadding="12dp" />
+
+        <TextView
+            android:id="@+id/tvCheckReplyHint"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_marginEnd="48dp"
+            android:text="@string/title_advanced_check_reply_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/swCheckReply" />
     </androidx.constraintlayout.widget.ConstraintLayout>
 </ScrollView>
\ No newline at end of file
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 0f0c7c1a32..967fa62424 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -391,6 +391,7 @@
     <string name="title_advanced_poll_hint">Synchronizing periodically will compare local and remote messages each and every time, which is an expensive operation possibly resulting in extra battery usage, especially when there are a lot of messages to synchronize. Always synchronizing will avoid this by continuous monitoring for changes only.</string>
     <string name="title_advanced_schedule_hint">Tap on a time to set a time</string>
     <string name="title_advanced_check_mx">Check sender email addresses on synchronizing messages</string>
+    <string name="title_advanced_check_reply">Check reply email addresses on synchronizing messages</string>
     <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_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_sync_folders_hint">Disabling this will reduce data and battery usage somewhat, but will disable updating the list of folders too</string>
@@ -398,6 +399,7 @@
 
     <string name="title_advanced_suggest_local_hint">In addition to contacts provided by Android. Contact data will be stored for newly sent or received messages only when enabled.</string>
     <string name="title_advanced_lookup_mx_hint">This will check if DNS MX records exist</string>
+    <string name="title_advanced_check_reply_hint">This will check if domain name of the sender and reply addresses are the same</string>
 
     <string name="title_advanced_metered_hint">Metered connections are generally mobile connections or paid Wi-Fi hotspots</string>
     <string name="title_advanced_metered_warning">Disabling this option will disable receiving and sending messages on mobile internet connections</string>
@@ -506,6 +508,7 @@
     <string name="title_no_idle">This provider does not support push messages. This will delay reception of new messages and increase battery usage.</string>
     <string name="title_no_utf8">This provider does not support UTF-8</string>
     <string name="title_no_sync">Synchronization errors since %1$s</string>
+    <string name="title_reply_domain">The sender (%1$s) and reply domain (%2$s) differ</string>
     <string name="title_identity_required">An identity is required to send messages</string>
     <string name="title_drafts_required">A drafts folder is required to send messages</string>
     <string name="title_account_delete">Delete this account permanently?</string>