Use more simple email validation regex

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/CreateKeyEmailFragment.java

@@ -26,7 +26,6 @@ import android.support.v4.app.Fragment;
 import android.support.v7.widget.DefaultItemAnimator;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
-import android.util.Patterns;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -52,6 +51,10 @@ public class CreateKeyEmailFragment extends Fragment {
     private ArrayList<EmailAdapter.ViewModel> mAdditionalEmailModels;
     private EmailAdapter mEmailAdapter;
 
+    // NOTE: Do not use more complicated pattern like defined in android.util.Patterns.EMAIL_ADDRESS
+    // EMAIL_ADDRESS fails for mails with umlauts for example
+    private static final Pattern EMAIL_PATTERN = Pattern.compile(".[\\S]+@.[\\S]+\\.[a-z]+");
+
     /**
      * Creates new instance of this fragment
      */
@@ -174,10 +177,8 @@ public class CreateKeyEmailFragment extends Fragment {
      * @return
      */
     private boolean isEmailFormatValid(String email) {
-        Pattern emailPattern = Patterns.EMAIL_ADDRESS;
-
         // check for email format or if the user did any input
-        return !(email.length() == 0 || !emailPattern.matcher(email).matches());
+        return !(email.length() == 0 || !EMAIL_PATTERN.matcher(email).matches());
     }
 
     /**