diff --git a/src/com/android/phone/common/mail/MailTransport.java b/src/com/android/phone/common/mail/MailTransport.java
index 172d1a9..a303036 100644
--- a/src/com/android/phone/common/mail/MailTransport.java
+++ b/src/com/android/phone/common/mail/MailTransport.java
@@ -18,20 +18,10 @@
 import android.content.Context;
 import android.net.Network;
 
+import com.android.internal.annotations.VisibleForTesting;
 import com.android.phone.common.mail.store.ImapStore;
 import com.android.phone.common.mail.utils.LogUtils;
 
-import java.net.SocketAddress;
-import java.util.ArrayList;
-import java.util.List;
-
-import javax.net.ssl.HostnameVerifier;
-import javax.net.ssl.HttpsURLConnection;
-import javax.net.ssl.SSLException;
-import javax.net.ssl.SSLPeerUnverifiedException;
-import javax.net.ssl.SSLSession;
-import javax.net.ssl.SSLSocket;
-
 import java.io.BufferedInputStream;
 import java.io.BufferedOutputStream;
 import java.io.IOException;
@@ -40,6 +30,15 @@
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.Socket;
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.net.ssl.HostnameVerifier;
+import javax.net.ssl.HttpsURLConnection;
+import javax.net.ssl.SSLException;
+import javax.net.ssl.SSLPeerUnverifiedException;
+import javax.net.ssl.SSLSession;
+import javax.net.ssl.SSLSocket;
 
 /**
  * Make connection and perform operations on mail server by reading and writing lines.
@@ -62,6 +61,7 @@
     private BufferedInputStream mIn;
     private BufferedOutputStream mOut;
     private int mFlags;
+    private SocketCreator mSocketCreator;
 
     public MailTransport(Context context, Network network, String address, int port, int flags) {
         mContext = context;
@@ -92,44 +92,57 @@
      * Attempts to open a connection using the Uri supplied for connection parameters.  Will attempt
      * an SSL connection if indicated.
      */
-    public void open() throws MessagingException, CertificateValidationException {
+    public void open() throws MessagingException {
         LogUtils.d(TAG, "*** IMAP open " + mHost + ":" + String.valueOf(mPort));
 
-        List<SocketAddress> socketAddresses = new ArrayList<SocketAddress>();
-        try {
-            if (canTrySslSecurity()) {
-                mSocket = HttpsURLConnection.getDefaultSSLSocketFactory().createSocket();
-                socketAddresses.add(new InetSocketAddress(mHost, mPort));
-            } else {
-                if (mNetwork == null) {
-                    mSocket = new Socket();
-                    socketAddresses.add(new InetSocketAddress(mHost, mPort));
-                } else {
-                    InetAddress[] inetAddresses = mNetwork.getAllByName(mHost);
-                    for (int i = 0; i < inetAddresses.length; i++) {
-                        socketAddresses.add(new InetSocketAddress(inetAddresses[i], mPort));
-                    }
-                    mSocket = mNetwork.getSocketFactory().createSocket();
+        List<InetSocketAddress> socketAddresses = new ArrayList<InetSocketAddress>();
+
+        if (mNetwork == null) {
+            socketAddresses.add(new InetSocketAddress(mHost, mPort));
+        } else {
+            try {
+                InetAddress[] inetAddresses = mNetwork.getAllByName(mHost);
+                if (inetAddresses.length == 0) {
+                    throw new MessagingException(MessagingException.IOERROR,
+                            "Host name " + mHost + "cannot be resolved on designated network");
                 }
+                for (int i = 0; i < inetAddresses.length; i++) {
+                    socketAddresses.add(new InetSocketAddress(inetAddresses[i], mPort));
+                }
+            } catch (IOException ioe) {
+                LogUtils.d(TAG, ioe.toString());
+                throw new MessagingException(MessagingException.IOERROR, ioe.toString());
             }
-        } catch (IOException ioe) {
-            LogUtils.d(TAG, ioe.toString());
-            throw new MessagingException(MessagingException.IOERROR, ioe.toString());
         }
 
+        boolean success = false;
         while (socketAddresses.size() > 0) {
+            mSocket = createSocket();
             try {
-                mSocket.connect(socketAddresses.remove(0), SOCKET_CONNECT_TIMEOUT);
+                InetSocketAddress address = socketAddresses.remove(0);
+                mSocket.connect(address, SOCKET_CONNECT_TIMEOUT);
 
-                // After the socket connects to an SSL server, confirm that the hostname is as
-                // expected
-                if (canTrySslSecurity() && !canTrustAllCertificates()) {
-                    verifyHostname(mSocket, mHost);
+                if (canTrySslSecurity()) {
+                    /**
+                     * {@link SSLSocket} must connect in its constructor, or create through a
+                     * already connected socket. Since we need to use
+                     * {@link Socket#connect(SocketAddress, int) } to set timeout, we can only
+                     * create it here.
+                     */
+                    LogUtils.d(TAG, "open: converting to SSL socket");
+                    mSocket = HttpsURLConnection.getDefaultSSLSocketFactory()
+                            .createSocket(mSocket, address.getHostName(), address.getPort(), true);
+                    // After the socket connects to an SSL server, confirm that the hostname is as
+                    // expected
+                    if (!canTrustAllCertificates()) {
+                        verifyHostname(mSocket, mHost);
+                    }
                 }
 
                 mIn = new BufferedInputStream(mSocket.getInputStream(), 1024);
                 mOut = new BufferedOutputStream(mSocket.getOutputStream(), 512);
                 mSocket.setSoTimeout(SOCKET_READ_TIMEOUT);
+                success = true;
                 return;
             } catch (IOException ioe) {
                 LogUtils.d(TAG, ioe.toString());
@@ -137,10 +150,50 @@
                     // Only throw an error when there are no more sockets to try.
                     throw new MessagingException(MessagingException.IOERROR, ioe.toString());
                 }
+            } finally {
+                if (!success) {
+                    try {
+                        mSocket.close();
+                        mSocket = null;
+                    } catch (IOException ioe) {
+                        throw new MessagingException(MessagingException.IOERROR, ioe.toString());
+                    }
+
+                }
             }
         }
     }
 
+    // For testing. We need something that can replace the behavior of "new Socket()"
+    @VisibleForTesting
+    interface SocketCreator {
+        Socket createSocket() throws MessagingException;
+    }
+
+    @VisibleForTesting
+    void setSocketCreator(SocketCreator creator) {
+        mSocketCreator = creator;
+    }
+
+    protected Socket createSocket() throws MessagingException {
+        if (mSocketCreator != null) {
+            return mSocketCreator.createSocket();
+        }
+
+        if (mNetwork == null) {
+            LogUtils.v(TAG, "createSocket: network not specified");
+            return new Socket();
+        }
+
+        try {
+            LogUtils.v(TAG, "createSocket: network specified");
+            return mNetwork.getSocketFactory().createSocket();
+        } catch (IOException ioe) {
+            LogUtils.d(TAG, ioe.toString());
+            throw new MessagingException(MessagingException.IOERROR, ioe.toString());
+        }
+    }
+
     /**
      * Lightweight version of SSLCertificateSocketFactory.verifyHostname, which provides this
      * service but is not in the public API.
@@ -173,8 +226,8 @@
         // in the verifier code and is not available in the verifier API, and extracting the
         // CN & alts is beyond the scope of this patch.
         if (!HOSTNAME_VERIFIER.verify(hostname, session)) {
-            throw new SSLPeerUnverifiedException(
-                    "Certificate hostname not useable for server: " + hostname);
+            throw new SSLPeerUnverifiedException("Certificate hostname not useable for server: "
+                    + session.getPeerPrincipal());
         }
     }
 
diff --git a/tests/Android.mk b/tests/Android.mk
index a3a657b..6cc0355 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -27,4 +27,8 @@
 
 LOCAL_INSTRUMENTATION_FOR := TeleService
 
+LOCAL_STATIC_JAVA_LIBRARIES := \
+        android-support-test \
+        mockito-target
+
 include $(BUILD_PACKAGE)
diff --git a/tests/src/com/android/phone/MockitoHelper.java b/tests/src/com/android/phone/MockitoHelper.java
new file mode 100644
index 0000000..3da5d6e
--- /dev/null
+++ b/tests/src/com/android/phone/MockitoHelper.java
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.phone;
+
+import com.android.services.telephony.Log;
+
+/**
+ * Helper for Mockito-based test cases.
+ */
+public final class MockitoHelper {
+
+    private static final String TAG = "MockitoHelper";
+
+    private ClassLoader mOriginalClassLoader;
+    private Thread mContextThread;
+
+    /**
+     * Creates a new helper, which in turn will set the context classloader so it can load Mockito
+     * resources.
+     *
+     * @param packageClass test case class
+     */
+    public void setUp(Class<?> packageClass) throws Exception {
+        // makes a copy of the context classloader
+        mContextThread = Thread.currentThread();
+        mOriginalClassLoader = mContextThread.getContextClassLoader();
+        ClassLoader newClassLoader = packageClass.getClassLoader();
+        Log.v(TAG, "Changing context classloader from " + mOriginalClassLoader
+                + " to " + newClassLoader);
+        mContextThread.setContextClassLoader(newClassLoader);
+    }
+
+    /**
+     * Restores the context classloader to the previous value.
+     */
+    public void tearDown() throws Exception {
+        Log.v(TAG, "Restoring context classloader to " + mOriginalClassLoader);
+        mContextThread.setContextClassLoader(mOriginalClassLoader);
+    }
+}
\ No newline at end of file
diff --git a/tests/src/com/android/phone/common/mail/MailTransportTest.java b/tests/src/com/android/phone/common/mail/MailTransportTest.java
new file mode 100644
index 0000000..1fd6596
--- /dev/null
+++ b/tests/src/com/android/phone/common/mail/MailTransportTest.java
@@ -0,0 +1,389 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+package com.android.phone.common.mail;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import android.net.Network;
+import android.test.AndroidTestCase;
+
+import com.android.phone.MockitoHelper;
+import com.android.phone.common.mail.MailTransport.SocketCreator;
+import com.android.phone.common.mail.store.ImapStore;
+
+import junit.framework.AssertionFailedError;
+
+import org.mockito.MockitoAnnotations;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+import java.net.SocketAddress;
+import java.net.SocketException;
+import java.net.UnknownHostException;
+
+import javax.net.SocketFactory;
+
+public class MailTransportTest extends AndroidTestCase {
+
+    private static final String HOST_ADDRESS = "127.0.0.1";
+    private static final String INVALID_HOST_ADDRESS = "255.255.255.255";
+    private static final int HOST_PORT = 80;
+    private static final int HOST_FLAGS = 0;
+    // bypass verifyHostname() in open() by setting ImapStore.FLAG_TRUST_ALL
+    private static final int HOST_FLAGS_SSL = ImapStore.FLAG_SSL & ImapStore.FLAG_TRUST_ALL;
+    private static final InetAddress VALID_INET_ADDRESS = createInetAddress(HOST_ADDRESS);
+    private static final InetAddress INVALID_INET_ADDRESS = createInetAddress(INVALID_HOST_ADDRESS);
+
+    // ClassLoader need to be replaced for mockito to work.
+    private MockitoHelper mMokitoHelper = new MockitoHelper();
+
+    @Override
+    public void setUp() throws Exception {
+        super.setUp();
+        mMokitoHelper.setUp(getClass());
+        MockitoAnnotations.initMocks(this);
+    }
+
+    @Override
+    public void tearDown() throws Exception {
+        mMokitoHelper.tearDown();
+        super.tearDown();
+    }
+
+    public void testCreateSocket_anyNetwork() throws MessagingException {
+        // With no network, Socket#Socket() should be called.
+        MailTransport transport =
+                new MailTransport(getContext(), null, HOST_ADDRESS, HOST_PORT, HOST_FLAGS);
+        Socket socket = transport.createSocket();
+        assertTrue(socket != null);
+    }
+
+    public void testCreateSocket_networkSpecified() throws MessagingException, IOException {
+        // Network#getSocketFactory should be used to create socket.
+        Network mockNetwork = createMockNetwork();
+        MailTransport transport =
+                new MailTransport(getContext(), mockNetwork, HOST_ADDRESS, HOST_PORT, HOST_FLAGS);
+        Socket socket = transport.createSocket();
+        assertTrue(socket != null);
+        verify(mockNetwork).getSocketFactory();
+    }
+
+    public void testCreateSocket_socketCreator() throws MessagingException, IOException {
+        // For testing purposes, how sockets are created can be overridden.
+        SocketCreator socketCreator = new SocketCreator() {
+
+            private final Socket mSocket = new Socket();
+
+            @Override
+            public Socket createSocket() {
+                return mSocket;
+            }
+        };
+
+        MailTransport transport = new
+                MailTransport(getContext(), null, HOST_ADDRESS, HOST_PORT, HOST_FLAGS);
+
+        transport.setSocketCreator(socketCreator);
+
+        Socket socket = transport.createSocket();
+        assertTrue(socket == socketCreator.createSocket());
+    }
+
+    public void testOpen() throws MessagingException {
+        MailTransport transport = new MailTransport(getContext(), null, HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS);
+        transport.setSocketCreator(new TestSocketCreator());
+        transport.open();
+        assertTrue(transport.isOpen());
+
+    }
+
+    public void testOpen_Ssl() throws MessagingException {
+        //opening with ssl support.
+        MailTransport transport = new MailTransport(getContext(), null, HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS_SSL);
+        transport.setSocketCreator(new TestSocketCreator());
+        transport.open();
+        assertTrue(transport.isOpen());
+
+    }
+
+    public void testOpen_MultiIp() throws MessagingException {
+        //In case of round robin DNS, try all resolved address until one succeeded.
+        Network network = createMultiIpMockNetwork();
+        MailTransport transport = new MailTransport(getContext(), network, HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS);
+        transport.setSocketCreator(new TestSocketCreator());
+        transport.open();
+        assertTrue(transport.isOpen());
+    }
+
+    public void testOpen_MultiIp_SSL() throws MessagingException {
+        Network network = createMultiIpMockNetwork();
+
+        MailTransport transport = new MailTransport(getContext(), network, HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS_SSL);
+        transport.setSocketCreator(new TestSocketCreator());
+        transport.open();
+        assertTrue(transport.isOpen());
+    }
+
+    public void testOpen_network_hostResolutionFailed() {
+        // Couldn't resolve host on the network. Open() should fail.
+        Network network = createMockNetwork();
+        try {
+            when(network.getAllByName(HOST_ADDRESS))
+                    .thenThrow(new UnknownHostException("host resolution failed"));
+        } catch (IOException e) {
+            //ignored
+        }
+
+        MailTransport transport = new MailTransport(getContext(), network, HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS);
+        try {
+            transport.open();
+            throw new AssertionFailedError("Should throw MessagingException");
+        } catch (MessagingException e) {
+            //expected
+        }
+        assertFalse(transport.isOpen());
+    }
+
+    public void testOpen_createSocketFailed() {
+        // Unable to create socket. Open() should fail.
+        MailTransport transport = new MailTransport(getContext(), null, HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS);
+        transport.setSocketCreator(new SocketCreator() {
+            @Override
+            public Socket createSocket() throws MessagingException {
+                throw new MessagingException("createSocket failed");
+            }
+        });
+        try {
+            transport.open();
+            throw new AssertionFailedError("Should throw MessagingException");
+        } catch (MessagingException e) {
+            //expected
+        }
+        assertFalse(transport.isOpen());
+    }
+
+    public void testOpen_network_createSocketFailed() {
+        // Unable to create socket. Open() should fail.
+
+        Network network = createOneIpMockNetwork();
+        SocketFactory mockSocketFactory = mock(SocketFactory.class);
+        try {
+            when(mockSocketFactory.createSocket())
+                    .thenThrow(new IOException("unable to create socket"));
+        } catch (IOException e) {
+            //ignored
+        }
+        when(network.getSocketFactory()).thenReturn(mockSocketFactory);
+
+        MailTransport transport = new MailTransport(getContext(), network, HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS);
+
+        try {
+            transport.open();
+            throw new AssertionFailedError("Should throw MessagingException");
+        } catch (MessagingException e) {
+            //expected
+        }
+        assertFalse(transport.isOpen());
+    }
+
+    public void testOpen_connectFailed_one() {
+        // There is only one IP for this host, and we failed to connect to it. Open() should fail.
+
+        MailTransport transport = new MailTransport(getContext(), null, HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS);
+        transport.setSocketCreator(new SocketCreator() {
+            @Override
+            public Socket createSocket() throws MessagingException {
+                return new Socket() {
+                    @Override
+                    public void connect(SocketAddress address, int timeout) throws IOException {
+                        throw new IOException("connect failed");
+                    }
+                };
+            }
+        });
+        try {
+            transport.open();
+            throw new AssertionFailedError("Should throw MessagingException");
+        } catch (MessagingException e) {
+            //expected
+        }
+        assertFalse(transport.isOpen());
+    }
+
+    public void testOpen_connectFailed_multi() {
+        // There are multiple IP for this host, and we failed to connect to any of it.
+        // Open() should fail.
+        MailTransport transport = new MailTransport(getContext(), createMultiIpMockNetwork(),
+                HOST_ADDRESS,
+                HOST_PORT, HOST_FLAGS);
+        transport.setSocketCreator(new SocketCreator() {
+            @Override
+            public Socket createSocket() throws MessagingException {
+                return new Socket() {
+                    @Override
+                    public void connect(SocketAddress address, int timeout) throws IOException {
+                        throw new IOException("connect failed");
+                    }
+                };
+            }
+        });
+        try {
+            transport.open();
+            throw new AssertionFailedError("Should throw MessagingException");
+        } catch (MessagingException e) {
+            //expected
+        }
+        assertFalse(transport.isOpen());
+    }
+
+    private class TestSocket extends Socket {
+
+        boolean mConnected = false;
+
+
+        /**
+         * A make a mock connection to the address.
+         *
+         * @param address Only address equivalent to VALID_INET_ADDRESS or INVALID_INET_ADDRESS is
+         * accepted
+         * @param timeout Ignored but should >= 0.
+         */
+        @Override
+        public void connect(SocketAddress address, int timeout) throws IOException {
+            // copied from Socket#connect
+            if (isClosed()) {
+                throw new SocketException("Socket is closed");
+            }
+            if (timeout < 0) {
+                throw new IllegalArgumentException("timeout < 0");
+            }
+            if (isConnected()) {
+                throw new SocketException("Already connected");
+            }
+            if (address == null) {
+                throw new IllegalArgumentException("remoteAddr == null");
+            }
+
+            if (!(address instanceof InetSocketAddress)) {
+                throw new AssertionError("address should be InetSocketAddress");
+            }
+
+            InetSocketAddress inetSocketAddress = (InetSocketAddress) address;
+            if (inetSocketAddress.getAddress().equals(INVALID_INET_ADDRESS)) {
+                throw new IOException("invalid address");
+            } else if (inetSocketAddress.getAddress().equals(VALID_INET_ADDRESS)) {
+                mConnected = true;
+            } else {
+                throw new AssertionError("Only INVALID_ADDRESS or VALID_ADDRESS are allowed");
+            }
+        }
+
+        @Override
+        public boolean isConnected() {
+            return mConnected;
+        }
+
+    }
+
+
+    private class TestSocketCreator implements MailTransport.SocketCreator {
+
+        @Override
+        public Socket createSocket() throws MessagingException {
+            Socket socket = new TestSocket();
+            return socket;
+        }
+
+    }
+
+    /**
+     * @return a mock Network that can create a TestSocket with {@code getSocketFactory()
+     * .createSocket()}
+     */
+    private Network createMockNetwork() {
+        Network network = mock(Network.class);
+        SocketFactory mockSocketFactory = mock(SocketFactory.class);
+        try {
+            when(mockSocketFactory.createSocket()).thenReturn(new TestSocket());
+        } catch (IOException e) {
+            //ignored
+        }
+        when(network.getSocketFactory()).thenReturn(mockSocketFactory);
+        return network;
+    }
+
+    /**
+     * @return a mock Network like {@link MailTransportTest#createMockNetwork()}, but also supports
+     * {@link Network#getAllByName(String)} with one valid result.
+     */
+    private Network createOneIpMockNetwork() {
+        Network network = createMockNetwork();
+        try {
+            when(network.getAllByName(HOST_ADDRESS))
+                    .thenReturn(new InetAddress[] {VALID_INET_ADDRESS});
+        } catch (UnknownHostException e) {
+            //ignored
+        }
+
+        return network;
+    }
+
+    /**
+     * @return a mock Network like {@link MailTransportTest#createMockNetwork()}, but also supports
+     * {@link Network#getAllByName(String)}, which will return 2 address with the first one
+     * invalid.
+     */
+    private Network createMultiIpMockNetwork() {
+        Network network = createMockNetwork();
+        try {
+            when(network.getAllByName(HOST_ADDRESS))
+                    .thenReturn(new InetAddress[] {INVALID_INET_ADDRESS, VALID_INET_ADDRESS});
+        } catch (UnknownHostException e) {
+            //ignored
+        }
+
+        return network;
+    }
+
+    /**
+     * helper method to translate{@code host} into a InetAddress.
+     *
+     * @param host IP address of the host. Domain name should not be used as this method should not
+     * access the internet.
+     */
+    private static InetAddress createInetAddress(String host) {
+        try {
+            return InetAddress.getByName(host);
+        } catch (UnknownHostException e) {
+            return null;
+        }
+    }
+
+
+}