Tengo una app creada y una opción consiste en enviar un formulario en background usando javamail, el problema es que a la hora de añadir una imagen, la aplicación actúa como si enviase el mail correctamente pero en la bandeja de Gmail no recibo nada. Sin embargo, si envío el mismo email pero sin añadir una imagen adjunta si recibo perfectamente el correo. He mirado en mil sitios pero no encuentro la solucion al problema. Adjunto el código completo.

public class Correo extends AppCompatActivity implements LocationListener{  //Declaring EditText private EditText editTextSubject; private EditText editTextMessage; private EditText editTextNombre; private EditText editTextApellidos; private EditText editTextTelefono; /*public static final String Nombre = "NomKey"; public static final String Apellidos = "ApKey"; public static final String Asunto = "AsKey"; public static final String Mensaje = "MenKey"; public static final String Telefono = "TelKey"; public static final String mypreference = "mypref";*/  Button btnTackPic; ImageView ivThumbnailPhoto; Bitmap bitMap; static int TAKE_PICTURE = 1; private static final int PICK_IMAGE = 100; Uri imageUri; Button btngal; String rutaimg; LocationManager locationManager; Location location;  //Send button private Button buttonSend; Button btnUbicacion; String ubicacion; double latitud = 0; double longitud = 0; EditText editubi;  Bitmap bitimg; File imagefile; BodyPart adjunto = new MimeBodyPart(); Multipart multipart = new MimeMultipart();   @Override protected void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     getSupportActionBar().setDisplayHomeAsUpEnabled(true);     setContentView(R.layout.correo);       //Initializing the views     editTextSubject = (EditText) findViewById(R.id.editTextSubject);     editTextMessage = (EditText) findViewById(R.id.editTextMessage);     editTextNombre = (EditText) findViewById(R.id.editTextNombre);     editTextApellidos = (EditText) findViewById(R.id.editTextApellidos);     editTextTelefono = (EditText) findViewById(R.id.editTextTelefono);     editubi = (EditText) findViewById(R.id.editubi);      buttonSend = (Button) findViewById(R.id.buttonSend);     btnUbicacion = (Button) findViewById(R.id.btnUbicacion);      //Adding click listener     buttonSend.setOnClickListener(new View.OnClickListener() {         @Override         public void onClick(View v) {             sendEmail();         }     });     if (ContextCompat.checkSelfPermission(getApplicationContext(), android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getApplicationContext(), android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {          ActivityCompat.requestPermissions(this, new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION, android.Manifest.permission.ACCESS_COARSE_LOCATION}, 101);      }     btnUbicacion.setOnClickListener(new View.OnClickListener() {         @Override         public void onClick(View view) {             getLocation();     }      });;         btnTackPic = (Button) findViewById(R.id.btnTakePic);     ivThumbnailPhoto = (ImageView) findViewById(R.id.ivThumbnailPhoto);      // add onclick listener to the button     btnTackPic.setOnClickListener(new View.OnClickListener() {         @Override         public void onClick(View v) {             Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);              // start camera activity             startActivityForResult(intent, TAKE_PICTURE);         }     });      btngal = (Button) findViewById(R.id.btngal) ;      btngal.setOnClickListener(new View.OnClickListener() {         @Override         public void onClick(View v) {             openGallery();         }     });  } @Override protected void onActivityResult(int requestCode, int resultCode, Intent intent) {      if (requestCode == TAKE_PICTURE && resultCode== RESULT_OK && intent!=null){         // get bundle         bitMap = (Bitmap) intent.getExtras().get("data");         ivThumbnailPhoto.setImageBitmap(bitMap);      }      if(resultCode == RESULT_OK && requestCode == PICK_IMAGE){         imageUri = intent.getData();         imagefile = new File(getRealPathFromURI(imageUri));          ivThumbnailPhoto.setImageURI(imageUri);          try {             bitimg = MediaStore.Images.Media.getBitmap(this.getContentResolver(), imageUri);          } catch (IOException e) {             e.printStackTrace();         }     } }   private void openGallery(){     Intent gallery = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.INTERNAL_CONTENT_URI);     startActivityForResult(gallery, PICK_IMAGE); }   private void sendEmail() {     //Getting content for email     String email = "**********@gmail.com";     String subject = editTextSubject.getText().toString().trim();     String message = editTextMessage.getText().toString().trim();     String nombre = editTextNombre.getText().toString().trim();     String apellidos = editTextApellidos.getText().toString().trim();     String telefono = editTextTelefono.getText().toString().trim();     String ubiman = editubi.getText().toString().trim();      String msg = "Nombre: " + nombre + " " + apellidos + "\n" + "\n" + "Teléfono: " + telefono + "\n" + "\n" + "Asunto: " + subject + "\n" + "\n" + "Incidencia: " + message + "\n" + "\n" + "Ubicación manual : " + ubiman + "\n" + "\n" + "Ubicación GPS: " + ubicacion + "\n" + "\n" ;       /*if (subject.equals("") || message.equals("") || nombre.equals("") || apellidos.equals("") || telefono.equals("")) {         Toast.makeText(this, "Por favor, rellene todos los campos marcados con asterisco", Toast.LENGTH_SHORT).show();     }     else{*/         //Creating SendMail object         SendMail sm = new SendMail(this, email, subject, msg, imagefile);          //Executing sendmail to send email          sm.execute();         editTextMessage.setText("");         editTextSubject.setText("");         editTextTelefono.setText("");         editTextApellidos.setText("");         editTextNombre.setText("");     //}  } void getLocation() {     try {         locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);         locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 5000, 5,  this);     }     catch(SecurityException e) {         e.printStackTrace();     } } @Override public void onLocationChanged(Location location) {     latitud = location.getLatitude();     longitud = location.getLongitude();     ubicacion = "https://maps.google.com?q=" + latitud + "," + longitud;     if (latitud != 0 || longitud != 0) {         try {             Geocoder geocoder = new Geocoder(this, Locale.getDefault());             List<Address> list = geocoder.getFromLocation(                     latitud, longitud, 1);             if (!list.isEmpty()) {                 Address DirCalle = list.get(0);                 editubi.setText(DirCalle.getAddressLine(0));             }          } catch (IOException e) {             e.printStackTrace();         }     } } @Override public void onProviderDisabled(String provider) {     Toast.makeText(Correo.this, "Active el GPS y el Internet", Toast.LENGTH_SHORT).show(); } @Override public void onStatusChanged(String provider, int status, Bundle extras) {  } @Override public void onProviderEnabled(String provider) {  }  private String getRealPathFromURI(Uri contentURI) {     Cursor cursor = getContentResolver().query(contentURI, null, null, null, null);     if (cursor == null) { // Source is Dropbox or other similar local file path         return contentURI.getPath();     } else {         cursor.moveToFirst();         int idx = cursor.getColumnIndex(MediaStore.Images.ImageColumns.DATA);         return cursor.getString(idx);     } }  public boolean onOptionsItemSelected(MenuItem item) {     switch (item.getItemId()) {         case android.R.id.home: //hago un case por si en un futuro agrego mas opciones             Log.i("ActionBar", "Atrás!");             finish();             return true;         default:             return super.onOptionsItemSelected(item);     } }  } 

El archivo de imagen lo envío a la clase SendMail, donde se recibe perfectamente:

 public class SendMail extends AsyncTask<Void,Void,Void>  {  //Declaring Variables private Context context; private Session session;  //Information to send email private String email; private String subject; private String message; //private MimeMultipart Adjunto = new MimeMultipart(); private File imagefile;  //private BodyPart adjunto = new MimeBodyPart(); //private BodyPart texto = new MimeBodyPart();    //Progressdialog to show while sending email private ProgressDialog progressDialog; private Intent intent;  //Class Constructor public SendMail(Context context, String email, String subject, String message, File imagefile){     //Initializing variables     this.context = context;     this.email = email;     this.subject = subject;     this.message = message;     this.imagefile = imagefile; }  @Override protected void onPreExecute() {     super.onPreExecute();     //Showing progress dialog while sending email     progressDialog = ProgressDialog.show(context,"Enviando incidencia","Espere...",false,false); }  @Override protected void onPostExecute(Void aVoid) {     super.onPostExecute(aVoid);     //Dismissing the progress dialog     progressDialog.dismiss();     //Showing a success message     Toast.makeText(context,"Incidencia enviada",Toast.LENGTH_LONG).show(); }  @Override protected Void doInBackground(Void... params) {     //Creating properties     Properties props = new Properties();      //Configuring properties for gmail     //If you are not using gmail you may need to change the values     props.setProperty("mail.smtp.host", "smtp.gmail.com");     props.setProperty("mail.smtp.starttls.enable", "true");     props.setProperty("mail.smtp.port", "587");     props.setProperty("mail.smtp.user", "***********@gmail.com");     props.setProperty("mail.smtp.auth", "true");       //Creating a new session     session = Session.getDefaultInstance(props,             new javax.mail.Authenticator() {                 //Authenticating the password                 protected PasswordAuthentication getPasswordAuthentication() {                     return new PasswordAuthentication(Config.EMAIL, Config.PASSWORD);                 }             });       try {         //Creating MimeMessage object         MimeMessage mm = new MimeMessage(session);          MimeMultipart multipart = new MimeMultipart();          //Setting sender address         mm.setFrom(new InternetAddress(Config.EMAIL));         //Adding receiver         mm.addRecipient(Message.RecipientType.TO, new InternetAddress(email));         //Adding subject         mm.setSubject(subject);          mm.setText(message);          MimeBodyPart at = new MimeBodyPart();         at.setDisposition(MimeBodyPart.ATTACHMENT);         at.attachFile(imagefile);         at.setFileName("incidencia.jpg");          //multipart.addBodyPart(messageBodyPart);         multipart.addBodyPart(at);          //Adding message         mm.setContent(multipart);          Transport t = session.getTransport("smtp");         t.connect(Config.EMAIL,Config.PASSWORD);         t.sendMessage(mm,mm.getAllRecipients());         t.close();         //Sending email         //Transport.send(mm);      } catch (MessagingException e) {         e.printStackTrace();     } catch (IOException e) {         e.printStackTrace();     }     return null; }   }