diff --git a/app/src/main/java/eu/faircode/email/FragmentCompose.java b/app/src/main/java/eu/faircode/email/FragmentCompose.java
index 1e83407cac..80f479a9f5 100644
--- a/app/src/main/java/eu/faircode/email/FragmentCompose.java
+++ b/app/src/main/java/eu/faircode/email/FragmentCompose.java
@@ -114,6 +114,10 @@ import org.jsoup.nodes.Element;
 import org.openintents.openpgp.OpenPgpError;
 import org.openintents.openpgp.util.OpenPgpApi;
 import org.openintents.openpgp.util.OpenPgpServiceConnection;
+import org.xbill.DNS.Lookup;
+import org.xbill.DNS.SimpleResolver;
+import org.xbill.DNS.TextParseException;
+import org.xbill.DNS.Type;
 
 import java.io.BufferedOutputStream;
 import java.io.BufferedWriter;
@@ -125,6 +129,7 @@ import java.io.FileWriter;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.net.UnknownHostException;
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
@@ -2463,8 +2468,10 @@ public class FragmentCompose extends FragmentBase {
                     try {
                         ato = InternetAddress.parse(to);
                         if (action == R.id.action_send)
-                            for (InternetAddress address : ato)
+                            for (InternetAddress address : ato) {
                                 address.validate();
+                                lookup(address, context);
+                            }
                     } catch (AddressException ex) {
                         throw new AddressException(context.getString(R.string.title_address_parse_error,
                                 Helper.ellipsize(to, ADDRESS_ELLIPSIZE), ex.getMessage()));
@@ -2474,8 +2481,10 @@ public class FragmentCompose extends FragmentBase {
                     try {
                         acc = InternetAddress.parse(cc);
                         if (action == R.id.action_send)
-                            for (InternetAddress address : acc)
+                            for (InternetAddress address : acc) {
                                 address.validate();
+                                lookup(address, context);
+                            }
                     } catch (AddressException ex) {
                         throw new AddressException(context.getString(R.string.title_address_parse_error,
                                 Helper.ellipsize(cc, ADDRESS_ELLIPSIZE), ex.getMessage()));
@@ -2485,8 +2494,10 @@ public class FragmentCompose extends FragmentBase {
                     try {
                         abcc = InternetAddress.parse(bcc);
                         if (action == R.id.action_send)
-                            for (InternetAddress address : abcc)
+                            for (InternetAddress address : abcc) {
                                 address.validate();
+                                lookup(address, context);
+                            }
                     } catch (AddressException ex) {
                         throw new AddressException(context.getString(R.string.title_address_parse_error,
                                 Helper.ellipsize(bcc, ADDRESS_ELLIPSIZE), ex.getMessage()));
@@ -2743,7 +2754,29 @@ public class FragmentCompose extends FragmentBase {
                 Helper.unexpectedError(getFragmentManager(), ex);
         }
 
-        String getActionName(int id) {
+        private void lookup(InternetAddress address, Context context) throws TextParseException, UnknownHostException {
+            SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
+            boolean lookup_mx = prefs.getBoolean("lookup_mx", false);
+            if (!lookup_mx)
+                return;
+
+            String email = address.getAddress();
+            if (email == null || !email.contains("@"))
+                return;
+
+            String domain = email.split("@")[1];
+            Lookup lookup = new Lookup(domain, Type.MX);
+            SimpleResolver resolver = new SimpleResolver(Helper.DEFAULT_DNS);
+            lookup.setResolver(resolver);
+            Log.i("Lookup dns=" + domain + " @" + resolver.getAddress());
+
+            lookup.run();
+            if (lookup.getResult() == Lookup.HOST_NOT_FOUND ||
+                    lookup.getResult() == Lookup.TYPE_NOT_FOUND)
+                throw new IllegalArgumentException(context.getString(R.string.title_no_server, domain));
+        }
+
+        private String getActionName(int id) {
             switch (id) {
                 case R.id.action_delete:
                     return "delete";
diff --git a/app/src/main/java/eu/faircode/email/FragmentOptionsSend.java b/app/src/main/java/eu/faircode/email/FragmentOptionsSend.java
index 054d27abcd..f0aca15d83 100644
--- a/app/src/main/java/eu/faircode/email/FragmentOptionsSend.java
+++ b/app/src/main/java/eu/faircode/email/FragmentOptionsSend.java
@@ -45,11 +45,12 @@ public class FragmentOptionsSend extends FragmentBase implements SharedPreferenc
     private SwitchCompat swAutoResize;
     private Spinner spAutoResize;
     private TextView tvAutoResize;
+    private SwitchCompat swLookupMx;
     private SwitchCompat swAutoSend;
     private Spinner spSendDelayed;
 
     private final static String[] RESET_OPTIONS = new String[]{
-            "keyboard", "prefix_once", "plain_only", "autoresize", "resize", "autosend", "send_delayed"
+            "keyboard", "prefix_once", "plain_only", "autoresize", "resize", "lookup_mx", "autosend", "send_delayed"
     };
 
     @Override
@@ -68,6 +69,7 @@ public class FragmentOptionsSend extends FragmentBase implements SharedPreferenc
         swAutoResize = view.findViewById(R.id.swAutoResize);
         spAutoResize = view.findViewById(R.id.spAutoResize);
         tvAutoResize = view.findViewById(R.id.tvAutoResize);
+        swLookupMx = view.findViewById(R.id.swLookupMx);
         swAutoSend = view.findViewById(R.id.swAutoSend);
         spSendDelayed = view.findViewById(R.id.spSendDelayed);
 
@@ -120,6 +122,13 @@ public class FragmentOptionsSend extends FragmentBase implements SharedPreferenc
             }
         });
 
+        swLookupMx.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
+            @Override
+            public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
+                prefs.edit().putBoolean("lookup_mx", checked).apply();
+            }
+        });
+
         swAutoSend.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
             @Override
             public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
@@ -201,6 +210,7 @@ public class FragmentOptionsSend extends FragmentBase implements SharedPreferenc
             }
         spAutoResize.setEnabled(swAutoResize.isChecked());
 
+        swLookupMx.setChecked(prefs.getBoolean("lookup_mx", false));
         swAutoSend.setChecked(!prefs.getBoolean("autosend", false));
 
         int send_delayed = prefs.getInt("send_delayed", 0);
diff --git a/app/src/main/res/layout/fragment_options_send.xml b/app/src/main/res/layout/fragment_options_send.xml
index cf1f631fea..3ea055b721 100644
--- a/app/src/main/res/layout/fragment_options_send.xml
+++ b/app/src/main/res/layout/fragment_options_send.xml
@@ -82,6 +82,29 @@
                 app:layout_constraintStart_toEndOf="@id/spAutoResize"
                 app:layout_constraintTop_toTopOf="@id/spAutoResize" />
 
+            <androidx.appcompat.widget.SwitchCompat
+                android:id="@+id/swLookupMx"
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:layout_marginTop="12dp"
+                android:text="@string/title_advanced_lookup_mx"
+                app:layout_constraintEnd_toEndOf="parent"
+                app:layout_constraintStart_toStartOf="parent"
+                app:layout_constraintTop_toBottomOf="@id/spAutoResize"
+                app:switchPadding="12dp" />
+
+            <TextView
+                android:id="@+id/tvLookupMxHint"
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:layout_marginEnd="48dp"
+                android:text="@string/title_advanced_lookup_mx_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/swLookupMx" />
+
             <androidx.appcompat.widget.SwitchCompat
                 android:id="@+id/swAutoSend"
                 android:layout_width="0dp"
@@ -91,7 +114,7 @@
                 android:text="@string/title_advanced_autosend"
                 app:layout_constraintEnd_toEndOf="parent"
                 app:layout_constraintStart_toStartOf="parent"
-                app:layout_constraintTop_toBottomOf="@id/spAutoResize"
+                app:layout_constraintTop_toBottomOf="@id/tvLookupMxHint"
                 app:switchPadding="12dp" />
 
             <TextView
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 1b28f7a909..643789855e 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -193,6 +193,7 @@
     <string name="title_advanced_plain_only">Send plain text only by default</string>
     <string name="title_advanced_autoresize">Automatically resize attached and embedded images</string>
     <string name="title_advanced_resize_pixels">&lt; %1$d pixels</string>
+    <string name="title_advanced_lookup_mx">Check recipient email addresses before sending</string>
     <string name="title_advanced_autosend">Confirm sending messages</string>
     <string name="title_advanced_send_delayed">Delay sending messages</string>
 
@@ -270,6 +271,8 @@
     <string name="title_advanced_sync_kept_hint">This will transfer extra data and use extra battery power, especially if there are a lot of messages kept 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>
 
+    <string name="title_advanced_lookup_mx_hint">This will check if DNS MX records exist</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>
     <string name="title_advanced_rlah_hint">Assuming no roaming within the EU</string>
@@ -504,6 +507,7 @@
     <string name="title_save">Save</string>
     <string name="title_send">Send</string>
     <string name="title_send_at">Send at &#8230;</string>
+    <string name="title_no_server">No server found at \'%1$s\'</string>
 
     <string name="title_style_bold">Bold</string>
     <string name="title_style_italic">Italic</string>