class EmailExampleGetFormPage

class EmailExampleGetFormPage extends FormBase {
    
    /**
     * The mail manager.
     *
     * @var \Drupal\Core\Mail\MailManagerInterface
     */
    protected $mailManager;
    
    /**
     * The email validator.
     *
     * @var \Drupal\Component\Utility\EmailValidator
     */
    protected $emailValidator;
    
    /**
     * The language manager.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * Constructs a new EmailExampleGetFormPage.
     *
     * @param \Drupal\Core\Mail\MailManagerInterface $mail_manager
     *   The mail manager.
     * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
     *   The language manager.
     * @param \Drupal\Component\Utility\EmailValidator $email_validator
     *   The email validator.
     */
    public function __construct(MailManagerInterface $mail_manager, LanguageManagerInterface $language_manager, EmailValidator $email_validator) {
        $this->mailManager = $mail_manager;
        $this->languageManager = $language_manager;
        $this->emailValidator = $email_validator;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        $form = new static($container->get('plugin.manager.mail'), $container->get('language_manager'), $container->get('email.validator'));
        $form->setMessenger($container->get('messenger'));
        $form->setStringTranslation($container->get('string_translation'));
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'email_example';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['intro'] = [
            '#markup' => $this->t('Use this form to send a message to an e-mail address. No spamming!'),
        ];
        $form['email'] = [
            '#type' => 'textfield',
            '#title' => $this->t('E-mail address'),
            '#required' => TRUE,
        ];
        $form['message'] = [
            '#type' => 'textarea',
            '#title' => $this->t('Message'),
            '#required' => TRUE,
        ];
        $form['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Submit'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateForm(array &$form, FormStateInterface $form_state) {
        if (!$this->emailValidator
            ->isValid($form_state->getValue('email'))) {
            $form_state->setErrorByName('email', $this->t('That e-mail address is not valid.'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $form_values = $form_state->getValues();
        // All system mails need to specify the module and template key (mirrored
        // from hook_mail()) that the message they want to send comes from.
        $module = 'email_example';
        $key = 'contact_message';
        // Specify 'to' and 'from' addresses.
        $to = $form_values['email'];
        $from = $this->config('system.site')
            ->get('mail');
        // "params" loads in additional context for email content completion in
        // hook_mail(). In this case, we want to pass in the values the user entered
        // into the form, which include the message body in $form_values['message'].
        $params = $form_values;
        // The language of the e-mail. This will one of three values:
        // - $account->getPreferredLangcode(): Used for sending mail to a particular
        //   website user, so that the mail appears in their preferred language.
        // - \Drupal::currentUser()->getPreferredLangcode(): Used when sending a
        //   mail back to the user currently viewing the site. This will send it in
        //   the language they're currently using.
        // - \Drupal::languageManager()->getDefaultLanguage()->getId: Used when
        //   sending mail to a pre-existing, 'neutral' address, such as the system
        //   e-mail address, or when you're unsure of the language preferences of
        //   the intended recipient.
        //
        // Since in our case, we are sending a message to a random e-mail address
        // that is not necessarily tied to a user account, we will use the site's
        // default language.
        $language_code = $this->languageManager
            ->getDefaultLanguage()
            ->getId();
        // Whether or not to automatically send the mail when we call mail() on the
        // mail manager. This defaults to TRUE, and is normally what you want unless
        // you need to do additional processing before the mail manager sends the
        // message.
        $send_now = TRUE;
        // Send the mail, and check for success. Note that this does not guarantee
        // message delivery; only that there were no PHP-related issues encountered
        // while sending.
        $result = $this->mailManager
            ->mail($module, $key, $to, $language_code, $params, $from, $send_now);
        if ($result['result'] == TRUE) {
            $this->messenger()
                ->addMessage($this->t('Your message has been sent.'));
        }
        else {
            $this->messenger()
                ->addMessage($this->t('There was a problem sending your message and it was not sent.'), 'error');
        }
    }

}