$transport = $this->_transportBuilder
                                ->setTemplateIdentifier('customemail_email_template')
                                ->setTemplateOptions(
                                    [
                                        'area' => 'frontend',
                                        'store' => MagentoStoreModelStore::DEFAULT_STORE_ID,
                                    ]
                                    )

                                        ->setTemplateVars([
                                            'firstname' => $post['firstname'],
                                            'lastname' => $post['lastname'],
                                    ])

                                    ->setFrom($sender)
                                    ->addTo($sentToEmail,$sentToName);
                                    try{
                                    $transport->getTransport()->sendMessage();
                                    }catch(Exception $e){
                                        var_dump($e->getMessage());die();
                                    }
                                    $this->_inlineTranslation->resume();
                                    die("Sent mail");