Check for VPN

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

@@ -277,6 +277,24 @@ public class ConnectionHelper {
         return true;
     }
 
+    static boolean vpnActive(Context context) {
+        ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
+        if (cm == null)
+            return false;
+
+        try {
+            for (Network network : cm.getAllNetworks()) {
+                NetworkCapabilities caps = cm.getNetworkCapabilities(network);
+                if (caps != null && caps.hasTransport(NetworkCapabilities.TRANSPORT_VPN))
+                    return true;
+            }
+        } catch (Throwable ex) {
+            Log.w(ex);
+        }
+
+        return false;
+    }
+
     static boolean airplaneMode(Context context) {
         return Settings.System.getInt(context.getContentResolver(),
                 Settings.Global.AIRPLANE_MODE_ON, 0) != 0;

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

@@ -14,6 +14,8 @@ import androidx.preference.PreferenceManager;
 import com.sun.mail.imap.IMAPFolder;
 import com.sun.mail.imap.IMAPStore;
 import com.sun.mail.smtp.SMTPTransport;
+import com.sun.mail.util.MailConnectException;
+import com.sun.mail.util.SocketConnectException;
 
 import net.openid.appauth.AuthState;
 import net.openid.appauth.AuthorizationException;
@@ -329,6 +331,18 @@ public class EmailService implements AutoCloseable {
                 return authState.jsonSerializeString();
             } else
                 throw ex;
+        } catch (MailConnectException ex) {
+            if (ConnectionHelper.vpnActive(context)) {
+                MailConnectException mex = new MailConnectException(new SocketConnectException(
+                        "The might be caused by the VPN in use",
+                        new Exception(),
+                        ex.getHost(),
+                        ex.getPort(),
+                        ex.getConnectionTimeout()));
+                mex.setNextException(ex.getNextException());
+                throw mex;
+            } else
+                throw ex;
         }
     }
 

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

@@ -969,6 +969,8 @@ public class Log {
                 NetworkCapabilities caps = cm.getNetworkCapabilities(network);
                 size += write(os, (network.equals(active) ? "active=" : "network=") + network + " capabilities=" + caps + "\r\n\r\n");
             }
+
+            size += write(os, "VPN active=" + ConnectionHelper.vpnActive(context) + "\r\n\r\n");
         }
 
         db.attachment().setDownloaded(attachment.id, size);