diff --git a/app/src/main/java/eu/faircode/email/BoundaryCallbackMessages.java b/app/src/main/java/eu/faircode/email/BoundaryCallbackMessages.java
index 29fbe6e4c8..7968e7b5d6 100644
--- a/app/src/main/java/eu/faircode/email/BoundaryCallbackMessages.java
+++ b/app/src/main/java/eu/faircode/email/BoundaryCallbackMessages.java
@@ -282,7 +282,7 @@ public class BoundaryCallbackMessages extends PagedList.BoundaryCallback<TupleMe
 
                 Log.i("Boundary server connecting account=" + account.name);
                 istore = (IMAPStore) isession.getStore(protocol);
-                ConnectionHelper.connect(context, isession, istore, account);
+                ConnectionHelper.connect(context, istore, account);
 
                 Log.i("Boundary server opening folder=" + browsable.name);
                 ifolder = (IMAPFolder) istore.getFolder(browsable.name);
diff --git a/app/src/main/java/eu/faircode/email/ConnectionHelper.java b/app/src/main/java/eu/faircode/email/ConnectionHelper.java
index ac743c095a..704be6aeb4 100644
--- a/app/src/main/java/eu/faircode/email/ConnectionHelper.java
+++ b/app/src/main/java/eu/faircode/email/ConnectionHelper.java
@@ -16,11 +16,13 @@ import androidx.preference.PreferenceManager;
 import com.bugsnag.android.BreadcrumbType;
 import com.bugsnag.android.Bugsnag;
 import com.sun.mail.imap.IMAPStore;
+import com.sun.mail.smtp.SMTPTransport;
 
 import org.xbill.DNS.Lookup;
 import org.xbill.DNS.SimpleResolver;
 import org.xbill.DNS.Type;
 
+import java.lang.reflect.Field;
 import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
@@ -34,7 +36,6 @@ import java.util.Map;
 import javax.mail.Address;
 import javax.mail.MessagingException;
 import javax.mail.Session;
-import javax.mail.Transport;
 import javax.mail.internet.InternetAddress;
 
 public class ConnectionHelper {
@@ -258,15 +259,15 @@ public class ConnectionHelper {
         return true;
     }
 
-    static void connect(Context context, Session isession, IMAPStore istore, EntityAccount account) throws MessagingException {
-        connect(context, isession, istore, account.host, account.port, account.user, account.password);
+    static void connect(Context context, IMAPStore istore, EntityAccount account) throws MessagingException {
+        connect(context, istore, account.host, account.port, account.user, account.password);
     }
 
-    static void connect(Context context, Session isession, Transport itransport, EntityIdentity identity) throws MessagingException {
-        connect(context, isession, itransport, identity.host, identity.port, identity.user, identity.password);
+    static void connect(Context context, SMTPTransport itransport, EntityIdentity identity) throws MessagingException {
+        connect(context, itransport, identity.host, identity.port, identity.user, identity.password);
     }
 
-    static void connect(Context context, Session isession, IMAPStore istore, String host, int port, String user, String password) throws MessagingException {
+    static void connect(Context context, IMAPStore istore, String host, int port, String user, String password) throws MessagingException {
         try {
             istore.connect(host, port, user, password);
         } catch (MessagingException ex) {
@@ -275,6 +276,9 @@ public class ConnectionHelper {
 
             try {
                 Log.i("Binding to " + any4);
+                Field fSession = getDeclaredField(istore.getClass(), "session");
+                fSession.setAccessible(true);
+                Session isession = (Session) fSession.get(istore);
                 isession.getProperties().put("mail.imap.localaddress", any4);
                 isession.getProperties().put("mail.imaps.localaddress", any4);
                 istore.connect(host, port, user, password);
@@ -304,7 +308,7 @@ public class ConnectionHelper {
             }
     }
 
-    static void connect(Context context, Session isession, Transport itransport, String host, int port, String user, String password) throws MessagingException {
+    static void connect(Context context, SMTPTransport itransport, String host, int port, String user, String password) throws MessagingException {
         try {
             itransport.connect(host, port, user, password);
         } catch (MessagingException ex) {
@@ -313,6 +317,9 @@ public class ConnectionHelper {
 
             try {
                 Log.i("Binding to " + any4);
+                Field fSession = getDeclaredField(itransport.getClass(), "session");
+                fSession.setAccessible(true);
+                Session isession = (Session) fSession.get(itransport);
                 isession.getProperties().put("mail.smtp.localaddress", any4);
                 isession.getProperties().put("mail.smtps.localaddress", any4);
                 itransport.connect(host, port, user, password);
@@ -323,14 +330,28 @@ public class ConnectionHelper {
         }
     }
 
+    private static Field getDeclaredField(Class clazz, String name) throws NoSuchFieldException {
+        while (clazz != null) {
+            try {
+                return clazz.getDeclaredField(name);
+            } catch (NoSuchFieldException ex) {
+                clazz = clazz.getSuperclass();
+            }
+        }
+        throw new NoSuchFieldException(name);
+    }
+
     private static boolean hasIPv6(String host) {
+        boolean has = false;
         try {
-            for (InetAddress iaddr : InetAddress.getAllByName(host))
+            for (InetAddress iaddr : InetAddress.getAllByName(host)) {
+                Log.i(host + " resolves to " + iaddr);
                 if (iaddr instanceof Inet6Address)
-                    return true;
+                    has = true;
+            }
         } catch (UnknownHostException ignored) {
         }
-        return false;
+        return has;
     }
 
     static boolean airplaneMode(Context context) {
diff --git a/app/src/main/java/eu/faircode/email/FragmentAccount.java b/app/src/main/java/eu/faircode/email/FragmentAccount.java
index a9c5577c37..d501bc05a3 100644
--- a/app/src/main/java/eu/faircode/email/FragmentAccount.java
+++ b/app/src/main/java/eu/faircode/email/FragmentAccount.java
@@ -536,7 +536,7 @@ public class FragmentAccount extends FragmentBase {
                 Session isession = Session.getInstance(props, null);
                 isession.setDebug(true);
                 try (IMAPStore istore = (IMAPStore) isession.getStore("imap" + (starttls ? "" : "s"))) {
-                    ConnectionHelper.connect(context, isession, istore, host, Integer.parseInt(port), user, password);
+                    ConnectionHelper.connect(context, istore, host, Integer.parseInt(port), user, password);
 
                     result.idle = istore.hasCapability("IDLE");
 
@@ -893,7 +893,7 @@ public class FragmentAccount extends FragmentBase {
                     isession.setDebug(true);
 
                     try (IMAPStore istore = (IMAPStore) isession.getStore("imap" + (starttls ? "" : "s"))) {
-                        ConnectionHelper.connect(context, isession, istore, host, Integer.parseInt(port), user, password);
+                        ConnectionHelper.connect(context, istore, host, Integer.parseInt(port), user, password);
 
                         for (Folder ifolder : istore.getDefaultFolder().list("*")) {
                             // Check folder attributes
diff --git a/app/src/main/java/eu/faircode/email/FragmentIdentity.java b/app/src/main/java/eu/faircode/email/FragmentIdentity.java
index 3a9dd32e52..122cb558f4 100644
--- a/app/src/main/java/eu/faircode/email/FragmentIdentity.java
+++ b/app/src/main/java/eu/faircode/email/FragmentIdentity.java
@@ -63,6 +63,7 @@ import androidx.lifecycle.Lifecycle;
 
 import com.google.android.material.snackbar.Snackbar;
 import com.google.android.material.textfield.TextInputLayout;
+import com.sun.mail.smtp.SMTPTransport;
 
 import java.net.Inet4Address;
 import java.net.Inet6Address;
@@ -74,7 +75,6 @@ import java.util.Objects;
 import java.util.Properties;
 
 import javax.mail.Session;
-import javax.mail.Transport;
 
 import static android.app.Activity.RESULT_OK;
 import static com.google.android.material.textfield.TextInputLayout.END_ICON_NONE;
@@ -702,8 +702,8 @@ public class FragmentIdentity extends FragmentBase {
                     isession.setDebug(true);
 
                     // Create transport
-                    try (Transport itransport = isession.getTransport(protocol)) {
-                        ConnectionHelper.connect(context, isession, itransport, host, Integer.parseInt(port), user, password);
+                    try (SMTPTransport itransport = (SMTPTransport) isession.getTransport(protocol)) {
+                        ConnectionHelper.connect(context, itransport, host, Integer.parseInt(port), user, password);
                     }
                 }
 
diff --git a/app/src/main/java/eu/faircode/email/FragmentQuickSetup.java b/app/src/main/java/eu/faircode/email/FragmentQuickSetup.java
index ed0c19ebc8..c98ee3b48d 100644
--- a/app/src/main/java/eu/faircode/email/FragmentQuickSetup.java
+++ b/app/src/main/java/eu/faircode/email/FragmentQuickSetup.java
@@ -53,6 +53,7 @@ import com.google.android.material.snackbar.Snackbar;
 import com.google.android.material.textfield.TextInputLayout;
 import com.sun.mail.imap.IMAPFolder;
 import com.sun.mail.imap.IMAPStore;
+import com.sun.mail.smtp.SMTPTransport;
 
 import java.net.UnknownHostException;
 import java.util.ArrayList;
@@ -62,7 +63,6 @@ import java.util.Properties;
 
 import javax.mail.Folder;
 import javax.mail.Session;
-import javax.mail.Transport;
 
 import static android.app.Activity.RESULT_OK;
 
@@ -257,7 +257,7 @@ public class FragmentQuickSetup extends FragmentBase {
                     Session isession = Session.getInstance(props, null);
                     isession.setDebug(true);
                     try (IMAPStore istore = (IMAPStore) isession.getStore(provider.imap_starttls ? "imap" : "imaps")) {
-                        ConnectionHelper.connect(context, isession, istore, provider.imap_host, provider.imap_port, user, password);
+                        ConnectionHelper.connect(context, istore, provider.imap_host, provider.imap_port, user, password);
 
                         boolean inbox = false;
                         boolean drafts = false;
@@ -320,8 +320,8 @@ public class FragmentQuickSetup extends FragmentBase {
                     Properties props = MessageHelper.getSessionProperties(null, false);
                     Session isession = Session.getInstance(props, null);
                     isession.setDebug(true);
-                    try (Transport itransport = isession.getTransport(provider.smtp_starttls ? "smtp" : "smtps")) {
-                        ConnectionHelper.connect(context, isession, itransport, provider.smtp_host, provider.smtp_port, user, password);
+                    try (SMTPTransport itransport = (SMTPTransport) isession.getTransport(provider.smtp_starttls ? "smtp" : "smtps")) {
+                        ConnectionHelper.connect(context, itransport, provider.smtp_host, provider.smtp_port, user, password);
                     }
                 }
 
diff --git a/app/src/main/java/eu/faircode/email/ServiceSend.java b/app/src/main/java/eu/faircode/email/ServiceSend.java
index bfc70f7d86..28c726b5c0 100644
--- a/app/src/main/java/eu/faircode/email/ServiceSend.java
+++ b/app/src/main/java/eu/faircode/email/ServiceSend.java
@@ -36,6 +36,8 @@ import androidx.core.content.ContextCompat;
 import androidx.lifecycle.Observer;
 import androidx.preference.PreferenceManager;
 
+import com.sun.mail.smtp.SMTPTransport;
+
 import java.io.IOException;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
@@ -55,7 +57,6 @@ import javax.mail.MessageRemovedException;
 import javax.mail.MessagingException;
 import javax.mail.SendFailedException;
 import javax.mail.Session;
-import javax.mail.Transport;
 import javax.mail.internet.InternetAddress;
 import javax.mail.internet.MimeMessage;
 
@@ -364,10 +365,10 @@ public class ServiceSend extends ServiceBase {
         }
 
         // Create transport
-        try (Transport itransport = isession.getTransport(protocol)) {
+        try (SMTPTransport itransport = (SMTPTransport) isession.getTransport(protocol)) {
             // Connect transport
             db.identity().setIdentityState(ident.id, "connecting");
-            ConnectionHelper.connect(this, isession, itransport, ident);
+            ConnectionHelper.connect(this, itransport, ident);
             db.identity().setIdentityState(ident.id, "connected");
 
             // Send message
diff --git a/app/src/main/java/eu/faircode/email/ServiceSynchronize.java b/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
index 2d4398e826..b4b5a4350d 100644
--- a/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
+++ b/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
@@ -737,7 +737,7 @@ public class ServiceSynchronize extends ServiceBase {
                     db.account().setAccountState(account.id, "connecting");
 
                     try {
-                        ConnectionHelper.connect(this, isession, istore, account);
+                        ConnectionHelper.connect(this, istore, account);
                     } catch (Throwable ex) {
                         if (ex instanceof AuthenticationFailedException) {
                             NotificationManager nm = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);