for me when i want to save the customer's information I got this error 'Unable to send mail: Unknown error' , this is the method execute

PS : when i change 1 or 2 fields all work fine, but when i make change for 3 fields or more then the error is occurred

public function execute()
    {
        $returnToEdit = false;
        $originalRequestData = $this->getRequest()->getPostValue();

        $customerId = $this->getCurrentCustomerId();

        if ($originalRequestData) {
            try {
                // optional fields might be set in request for future processing by observers in other modules
                $customerData = $this->_extractCustomerData();
                $addressesData = $this->_extractCustomerAddressData($customerData);

                // Récupération du helper
                $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
                $helper = $objectManager->create('Mymodule\Customer\Helper\Data');

                if ($customerId) {
                    $currentCustomer = $this->_customerRepository->getById($customerId);
                    // Vérifie en cas de modification si mail du request est vide, et mail du client est généré.
                    if ($originalRequestData['customer']['email'] == '' && $helper->isGeneratedEmail($currentCustomer->getEmail())) {
                        // Récupère le mail bidon du client.
                        $customerData['email'] = $currentCustomer->getEmail();
                        $originalRequestData['customer']['email'] = $currentCustomer->getEmail();
                    }
                    $customerData = array_merge(
                        $this->customerMapper->toFlatArray($currentCustomer),
                        $customerData
                    );
                    $customerData['id'] = $customerId;
                }
                // Vérifie l'existence du numéro de téléphone
                $phoneExist = $helper->doesPhoneExist($customerData['telephone'], $customerId);
                if ($phoneExist) {
                    // Message
                    $this->messageManager->addError(
                        __(
                            'Il existe déjà un compte avec ce numéro de téléphone. Veuillez créer ce compte avec un numéro de téléphone différent ou appeler le Service Client (0805 691 213).'
                        )
                    );
                    $this->_getSession()->setCustomerFormData($originalRequestData);
                    $resultRedirect = $this->resultRedirectFactory->create();
                    if ($customerId) {
                        // Vérifie l'existence du numéro de téléphone
                        if (!$phoneExist){
                            $resultRedirect->setPath(
                                'customer/*/edit',
                                ['id' => $customerId, '_current' => true]
                            );
                        }else{
                            // Ajout d'attribut error dans l URL, pour rester sur le même formulaire
                            $resultRedirect->setPath(
                                'customer/*/edit',
                                ['id' => $customerId, '_current' => true, 'error'  => true]
                            );
                        }
                    } else {
                        $resultRedirect->setPath(
                            'customer/*/new',
                            ['_current' => true]
                        );
                    }
                    return $resultRedirect;
                }

                /** @var CustomerInterface $customer */
                $customer = $this->customerDataFactory->create();
                $this->dataObjectHelper->populateWithArray(
                    $customer,
                    $customerData,
                    \Magento\Customer\Api\Data\CustomerInterface::class
                );
                $addresses = [];
                foreach ($addressesData as $addressData) {
                    $region = isset($addressData['region']) ? $addressData['region'] : null;
                    $regionId = isset($addressData['region_id']) ? $addressData['region_id'] : null;
                    $addressData['region'] = [
                        'region' => $region,
                        'region_id' => $regionId,
                    ];
                    $addressDataObject = $this->addressDataFactory->create();
                    $this->dataObjectHelper->populateWithArray(
                        $addressDataObject,
                        $addressData,
                        \Magento\Customer\Api\Data\AddressInterface::class
                    );
                    $addresses[] = $addressDataObject;
                }

                $this->_eventManager->dispatch(
                    'adminhtml_customer_prepare_save',
                    ['customer' => $customer, 'request' => $this->getRequest()]
                );
                $customer->setAddresses($addresses);
                if (isset($customerData['sendemail_store_id'])) {
                    $customer->setStoreId($customerData['sendemail_store_id']);
                }

                if (!$customer->getEmail()) {
                    $customer->setEmail($helper->_getNewCustomerEmail());
                }

                if (isset($customerData['chanel'])) {
                    $customer->setData('chanel', $customerData['chanel']);
                }

                // Save customer
                if ($customerId) {
                    $this->_customerRepository->save($customer);

                    $this->getEmailNotification()->credentialsChanged($customer, $currentCustomer->getEmail());
                } else {
                    $customer = $this->customerAccountManagement->createAccount($customer);
                    $customerId = $customer->getId();
                }

                $isSubscribed = null;
                if ($this->_authorization->isAllowed(null)) {
                    $isSubscribed = $this->getRequest()->getPost('subscription');
                }
                if ($isSubscribed !== null) {
                    if ($isSubscribed !== '0') {
                        $this->_subscriberFactory->create()->subscribeCustomerById($customerId);
                    } else {
                        $this->_subscriberFactory->create()->unsubscribeCustomerById($customerId);
                    }
                }

                // After save
                $this->_eventManager->dispatch(
                    'adminhtml_customer_save_after',
                    ['customer' => $customer, 'request' => $this->getRequest()]
                );
                $this->_getSession()->unsCustomerFormData();
                // Done Saving customer, finish save action
                $this->_coreRegistry->register(RegistryConstants::CURRENT_CUSTOMER_ID, $customerId);
                $this->messageManager->addSuccess(__('You saved the customer.'));
                $returnToEdit = (bool)$this->getRequest()->getParam('back', false);
            } catch (\Magento\Framework\Validator\Exception $exception) {
                $messages = $exception->getMessages();
                if (empty($messages)) {
                    $messages = $exception->getMessage();
                }
                $this->_addSessionErrorMessages($messages);
                $this->_getSession()->setCustomerFormData($originalRequestData);
                $returnToEdit = true;
            } catch (LocalizedException $exception) {
                $this->_addSessionErrorMessages($exception->getMessage());
                $this->_getSession()->setCustomerFormData($originalRequestData);
                $returnToEdit = true;
            } catch (\Exception $exception) {
                $this->messageManager->addException($exception, __('Something went wrong while saving the customer.'));
                $this->_getSession()->setCustomerFormData($originalRequestData);
                $returnToEdit = true;
            }
        }
        $resultRedirect = $this->resultRedirectFactory->create();
        if ($returnToEdit) {
            if ($customerId) {
                $resultRedirect->setPath(
                    'customer/*/edit',
                    ['id' => $customerId, '_current' => true]
                );
            } else {
                $resultRedirect->setPath(
                    'customer/*/new',
                    ['_current' => true]
                );
            }
        } else {
            $resultRedirect->setPath('customer/index');
        }
        return $resultRedirect;
    }