Lookup MX record for email domains

app/src/main/java/eu/faircode/email/AdapterMessage.java

@@ -3742,7 +3742,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
                         @Override
                         protected String[] onExecute(Context context, Bundle args) throws Throwable {
                             Uri uri = args.getParcelable("uri");
-                            return IPInfo.getOrganization(uri);
+                            return IPInfo.getOrganization(uri, context);
                         }
 
                         @Override

app/src/main/java/eu/faircode/email/ConnectionHelper.java

@@ -14,6 +14,8 @@ import android.telephony.TelephonyManager;
 import androidx.preference.PreferenceManager;
 
 import org.xbill.DNS.Lookup;
+import org.xbill.DNS.MXRecord;
+import org.xbill.DNS.Record;
 import org.xbill.DNS.SimpleResolver;
 import org.xbill.DNS.Type;
 
@@ -318,6 +320,28 @@ public class ConnectionHelper {
         return ok;
     }
 
+    static InetAddress lookupMx(String domain, Context context) {
+        try {
+            Lookup lookup = new Lookup(domain, Type.MX);
+            SimpleResolver resolver = new SimpleResolver(getDnsServer(context));
+            lookup.setResolver(resolver);
+            Log.i("Lookup MX=" + domain + " @" + resolver.getAddress());
+
+            lookup.run();
+            if (lookup.getResult() == Lookup.SUCCESSFUL) {
+                Record[] answers = lookup.getAnswers();
+                if (answers != null && answers.length > 0 && answers[0] instanceof MXRecord) {
+                    MXRecord mx = (MXRecord) answers[0];
+                    return InetAddress.getByName(mx.getTarget().toString(true));
+                }
+            }
+        } catch (Throwable ex) {
+            Log.w(ex);
+        }
+
+        return null;
+    }
+
     static boolean isSameDomain(String host1, String host2) {
         String domain1 = getDomain(host1);
         String domain2 = getDomain(host2);

app/src/main/java/eu/faircode/email/IPInfo.java

@@ -19,6 +19,7 @@ package eu.faircode.email;
     Copyright 2018-2019 by Marcel Bokhorst (M66B)
 */
 
+import android.content.Context;
 import android.net.MailTo;
 import android.net.ParseException;
 import android.net.Uri;
@@ -35,30 +36,33 @@ import java.util.Map;
 import javax.net.ssl.HttpsURLConnection;
 
 public class IPInfo {
-    private static Map<String, String> hostOrganization = new HashMap<>();
+    private static Map<InetAddress, String> hostOrganization = new HashMap<>();
 
-    static String[] getOrganization(Uri uri) throws IOException, ParseException {
+    static String[] getOrganization(Uri uri, Context context) throws IOException, ParseException {
         if ("mailto".equals(uri.getScheme())) {
             MailTo email = MailTo.parse(uri.toString());
             String to = email.getTo();
             if (to == null || !to.contains("@"))
                 throw new UnknownHostException();
-            String host = to.substring(to.indexOf('@') + 1);
-            return getOrganization(host);
+            String domain = to.substring(to.indexOf('@') + 1);
+            InetAddress address = ConnectionHelper.lookupMx(domain, context);
+            if (address == null)
+                throw new UnknownHostException();
+            return new String[]{domain, getOrganization(address)};
         } else {
             String host = uri.getHost();
             if (host == null)
                 throw new UnknownHostException();
-            return getOrganization(host);
+            InetAddress address = InetAddress.getByName(host);
+            return new String[]{host, getOrganization(address)};
         }
     }
 
-    private static String[] getOrganization(String host) throws IOException {
+    private static String getOrganization(InetAddress address) throws IOException {
         synchronized (hostOrganization) {
-            if (hostOrganization.containsKey(host))
-                return new String[]{host, hostOrganization.get(host)};
+            if (hostOrganization.containsKey(address))
+                return hostOrganization.get(address);
         }
-        InetAddress address = InetAddress.getByName(host);
         URL url = new URL("https://ipinfo.io/" + address.getHostAddress() + "/org");
         Log.i("GET " + url);
         HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
@@ -70,9 +74,9 @@ public class IPInfo {
             if ("undefined".equals(organization))
                 organization = null;
             synchronized (hostOrganization) {
-                hostOrganization.put(host, organization);
+                hostOrganization.put(address, organization);
             }
-            return new String[]{host, organization};
+            return organization;
         }
     }
 }