interface MailInterface

interface MailInterface {
    
    /**
     * Formats a message prior to sending.
     *
     * Allows to preprocess, format, and postprocess a mail message before it is
     * passed to the sending system. The message body is received as an array of
     * lines that are either strings or objects implementing
     * \Drupal\Component\Render\MarkupInterface. It must be converted to the
     * format expected by mail() which is a single string that can be either
     * plain text or HTML. In the HTML case an alternate plain-text version can
     * be returned in $message['plain'].
     *
     * The conversion process consists of the following steps:
     * - If the output is HTML then convert any input line that is a string using
     *   \Drupal\Component\Utility\Html\Html::Escape().
     * - If the output is plain text then convert any input line that is markup
     *   using \Drupal\Core\Mail\MailFormatHelper::htmlToText().
     * - Join the input lines into a single string.
     * - Wrap long lines using \Drupal\Core\Mail\MailFormatHelper::wrapMail().
     *
     * @param array $message
     *   A message array, as described in hook_mail_alter().
     *
     * @return array
     *   The formatted $message.
     *
     * @see \Drupal\Core\Mail\MailManagerInterface
     */
    public function format(array $message);
    
    /**
     * Sends a message composed by \Drupal\Core\Mail\MailManagerInterface->mail().
     *
     * @param array $message
     *   Message array with at least the following elements:
     *   - id: A unique identifier of the email type. Examples: 'contact_user_copy',
     *     'user_password_reset'.
     *   - to: The mail address or addresses where the message will be sent to.
     *     The formatting of this string will be validated with the
     *     @link http://php.net/manual/filter.filters.validate.php PHP email validation filter. @endlink
     *     Some examples:
     *     - user@example.com
     *     - user@example.com, anotheruser@example.com
     *     - User <user@example.com>
     *     - User <user@example.com>, Another User <anotheruser@example.com>
     *   - subject: Subject of the email to be sent. This must not contain any
     *     newline characters, or the mail may not be sent properly. The subject
     *     is converted to plain text by the mail plugin manager.
     *   - body: Message to be sent. Accepts both CRLF and LF line-endings.
     *     Email bodies must be wrapped. For smart plain text wrapping you can use
     *     \Drupal\Core\Mail\MailFormatHelper::wrapMail() .
     *   - headers: Associative array containing all additional mail headers not
     *     defined by one of the other parameters.  PHP's mail() looks for Cc and
     *     Bcc headers and sends the mail to addresses in these headers too.
     *
     * @return bool
     *   TRUE if the mail was successfully accepted for delivery, otherwise FALSE.
     */
    public function mail(array $message);

}