How to reconfigure the script for sending mail from the site to work via SMTP?

Question

PHP

Good afternoon.
There is a script for sending mail from the site. Letters go through the standard php mail function.
How can I choose to send via SMTP by default? The script contains both php mail and smtp. At what stage is the definition of how to send?
I will insert only part of the code - restriction.

const MAIL_TRANSPORT_SMTP = 1;
    const MAIL_TRANSPORT_DAEMON = 2;
    const MAIL_TRANSPORT_FAKE_SUCCESS = 3;
    const MAIL_TRANSPORT_FAKE_ERROR = 4;

    private static $connect = array('host' => 'smtp.mail.ru', 'port' => 465, 'login' => 'ЛОГИН', 'pass' => 'ПАРОЛЬ', 'fromru' => 'Mail');
    private $data = array(
        'to_email' => '', 'to_name' => '', 'from_name' => '', 'from_email' => '', 'as_plain' => false,
        'reply_email' => '', 'reply_name' => '', 'text' => '', 'subject' => '',
        'transport' => self::MAIL_TRANSPORT_DAEMON
    );
/**
     * 
     * @return bool
     */
    public function send() {
        $result = false;
        
        if (!$this->data['as_plain'] && is_file($_SERVER['DOCUMENT_ROOT'] . '/theme/default/mail.tpl')) {
            ob_start();
            if (!class_exists('ModCity')) {
                include_once $_SERVER['DOCUMENT_ROOT'] . '/ext/city/modcity.class.php';
            }
            $toEmail = $this->data['to_email'];
            $httpHost = 'http://' . $_SERVER['HTTP_HOST'];
            $mailContent = $this->data['text'];
            include $_SERVER['DOCUMENT_ROOT'] . '/theme/default/mail.tpl';
            $this->data['text'] = ob_get_clean();

            $siteParams = SFCore::siteParam();
            foreach ($siteParams as $paramAlias => $paramValue) {
                $this->data['text'] = str_replace('{' . $paramAlias . '}', $paramValue, $this->data['text']);
            }
            $this->data['text'] = str_replace('{year}', date('Y'), $this->data['text']);
        }
        $this->data['text_utf8'] = $this->data['text'];
        
        if (md5(@iconv('utf-8', 'utf-8', $this->data['subject'])) == md5($this->data['subject'])) {
            $this->data['subject'] = @iconv('utf-8', 'windows-1251', $this->data['subject']);
        }
        if (md5(@iconv('utf-8', 'utf-8', $this->data['text'])) == md5($this->data['text'])) {
            $this->data['text'] = @iconv('utf-8', 'windows-1251', $this->data['text']);
        }

        $toName = $this->data['to_name'];
        if ($toName && md5(@iconv('utf-8', 'utf-8', $toName)) == md5($toName)) {
            $toName = @iconv('utf-8', 'windows-1251', $toName);
        }
        $toEnc = '=?windows-1251?B?' . base64_encode($toName) . '?=';
        $this->data['to_full'] = "$toEnc <{$this->data['to_email']}>";

        $fromName = $this->data['from_name'];
        if ($fromName && md5(@iconv('utf-8', 'utf-8', $fromName)) == md5($fromName)) {
            $fromName = @iconv('utf-8', 'windows-1251', $fromName);
        }
        $fromEnc = '=?windows-1251?B?' . base64_encode($fromName) . '?=';
        $this->data['from_full'] = "$fromEnc <{$this->data['from_email']}>";

        if ($this->data['reply_email']) {
            $replyName = $this->data['reply_name'];
            if ($replyName && md5(@iconv('utf-8', 'utf-8', $replyName)) == md5($replyName)) {
                $replyName = @iconv('utf-8', 'windows-1251', $replyName);
            }
            $replyEnc = '=?windows-1251?B?' . base64_encode($replyName) . '?=';
            $this->data['reply_full'] = "$replyEnc <{$this->data['reply_email']}>";
        }

        $this->data['subject_ready'] = '=?windows-1251?B?' . base64_encode($this->data['subject']) . '?=';

        switch ($this->data['transport']) {
            case self::MAIL_TRANSPORT_SMTP: $result = $this->sendSMTP();
                break;
            case self::MAIL_TRANSPORT_DAEMON: $result = $this->sendDaemon();
                break;
            case self::MAIL_TRANSPORT_FAKE_SUCCESS: $result = true;
                break;
            case self::MAIL_TRANSPORT_FAKE_ERROR: default: $result = false;
        }

        $this->toLog($result);

        return $result;
    }

    private function toLog($result) {
        $q = "DELETE FROM mail_log WHERE ADDDATE(time_create,INTERVAL 1 MONTH) < NOW()";
        SFDB::query($q);
        $set = array("mail_from = '" . SFDB::escape($this->data['from_full']) . "', email = '" . SFDB::escape($this->data['to_full']) . "'");
        $set[] = "text = '" . SFDB::escape($this->data['text_utf8']) . "', subject = '" . SFDB::escape($this->data['subject_ready']) . "'";
        $set[] = "success = " . (int) $result . ", transport = {$this->data['transport']}";
        if (!empty($this->data['reply_full'])) {
            $set[] = "reply_to = '" . SFDB::escape($this->data['reply_full']) . "'";
        }
        $q = "INSERT INTO mail_log SET " . implode(', ', $set);
        $success = SFDB::query($q);
    }

    /**
     * Отправка через стандартную функцию php mail
     * @return type
     */
    private function sendDaemon() {
        $contentType = $this->data['as_plain'] ? 'plain' : 'html';
        $header = "Content-type: text/$contentType; charset=\"windows-1251\"\n";
        $header .= "MIME-Version: 1.0" . "\n";
        $header .= "From: {$this->data['from_full']}\n";
        if ($this->data['reply_email']) {
            $header .= "Reply-To: {$this->data['reply_full']}\n";
        }
        $header .= "Subject: {$this->data['subject_ready']}";
        //$header .= "Content-type: text/$contentType; charset=\"windows-1251\"\n";
        return mail($this->data['to_full'], $this->data['subject_ready'], $this->data['text'], $header);
    }

    /**
     * Отправка через SMTP
     * @return bool 
     */
    private function sendSMTP() {

        $canSend = true;
        if (empty(self::$connect['login'])) {
            $sender = explode(':', SFCore::siteParam('sender'));
            self::$connect['login'] = $sender[0];
            if (isset($sender[1])) {
                self::$connect['pass'] = $sender[1];
            } else {
                $canSend = false;
            }
        }
        if (!$canSend) {
            return false;
        }

        include_once dirname(__FILE__) . '/smtp_sasl/login_sasl_client.php';
        include_once dirname(__FILE__) . '/smtp_sasl/sasl.php';
        include_once dirname(__FILE__) . '/smtp.class.php';
        $smtp = new smtp();

        $sender_line = __LINE__;
        $recipient_line = __LINE__;

        $smtp->host_name = self::$connect['host'];
        $smtp->host_port = self::$connect['port'];
        $smtp->ssl = 1;
        $smtp->start_tls = 0;
        $smtp->localhost = "localhost";
        $smtp->timeout = 10;
        $smtp->data_timeout = 0;
        $smtp->debug = (int) @$_ENV['debug'];
        $smtp->html_debug = (int) @$_ENV['debug'];
        $smtp->pop3_auth_host = '';
        $smtp->user = self::$connect['login'];
        $smtp->realm = "";
        $smtp->password = self::$connect['pass'];
        $smtp->workstation = "";
        $smtp->authentication_mechanism = '';

        setlocale(LC_TIME, null);
        $date = strftime("%a, %d %b %Y %H:%M:%S %z");

        $contentType = $this->data['as_plain'] ? 'plain' : 'html';
        $headers = array(
            "From: {$this->data['from_full']}",
            "To: {$this->data['to_full']}",
            "Subject: {$this->data['subject_ready']}",
            "Date: " . $date,
            "Content-type: text/$contentType; charset=windows-1251"
        );
        if ($this->data['reply_email']) {
            $headers[] = "Reply-To: {$this->data['reply_full']}";
        }

        $res = $smtp->SendMessage(self::$connect['login'], array($this->data['to_email']), $headers, $this->data['text']);
        if(@$_ENV['debug']){
            echo $smtp->error;
        }
        return $res;
    }

Answer 1

switch ($this->data['transport']) {
            case self::MAIL_TRANSPORT_SMTP: $result = $this->sendSMTP();
                break;
            case self::MAIL_TRANSPORT_DAEMON: $result = $this->sendDaemon();
                break;
            case self::MAIL_TRANSPORT_FAKE_SUCCESS: $result = true;
                break;
            case self::MAIL_TRANSPORT_FAKE_ERROR: default: $result = false;
        }

Answer 2

Yes, here it’s actually possible and easier to do, put such a plugin https://wordpress.org/plugins/smtp-mailer-wp/ and it will definitely help with setting up smtp in order to replace the site’s mail with an external one qualitatively and so that it really improves the situation with mailing lists, especially relevant for those sites where you need a reg or mailing list of news by mail, here literally without such a plugin there is simply nowhere