Php 第一次发送邮件时延迟4分钟

我有一个确认电子邮件地址的表格。正确引入电子邮件后，php会在引入的电子邮件上发送邮件。必须在几秒钟内送达但需在4分钟内送达的邮件

<?

$headers = "MIME-Version: 1.0" . "\r\n";
$headers .= "Content-type:text/html;charset=UTF-8" . "\r\n";
$headers .= "From: Электронный дневник 8 'Б' <inbox@domain.site>" . "\r\n";
if(isset($_POST['submit_email'])){
    if (preg_match("/^(?:[a-z0-9]+(?:[-_.]?[a-z0-9]+)?@[a-z0-9_.-]+(?:\.?[a-z0-9]+)?\.[a-z]{2,5})$/i", $_POST['email'])) {// пароль
        //$activation=md5($_POST['email'].time()); // email + timestamp
        $activation=md5($_POST['email'].time());
        $count=mysqli_query($c,"SELECT login FROM pass WHERE email='".$_POST['email']."'");

        if(mysqli_num_rows($count) < 1)
        {
            mysqli_query($c,"UPDATE pass SET email = '".$_POST['email']."',activation_temp = '".$activation."' WHERE login = '".$_SESSION['User_em']."' "); //'".$_SESSION['User_em']."'
            unset($_SESSION['smth']);
            $_SESSION['confirm'] = $activation;
            mail("".$_POST['email']."", "Проверка Email", "Здравствуйте! <br/> Перейдите по ссылке , чтобы подтвердить электронную почту дневника. <br/> <a href = 'https://www.domain.site/confirm?code=".$activation."'>https://www.lyceummb8b.online/confirm?code=".$activation." </a>", $headers , "-finbox@domain.site");
            header('Location: pleasement');


        }
        else{
            header('Location: email?exist_error');

        }

    }
    else{
        header('Location: email?invalid_input');
    }


}


if(isset($_GET['invalid_input'])){
    $errors[] .= "Адрес указан не правильно. Проверьте правильность написания email. <br>";
}

if(isset($_GET['exist_error'])){
    $errors[] = 'Данный email уже существует.';
}

?>

<form class="form" role="form" autocomplete="off" id="formLogin" novalidate="" method="POST">
    <div class="form-group">
        <label>E-mail</label>
        <input type="email" class="form-control form-control-lg rounded
-0" id="pwd1" required="" autocomplete="new-password" name = "email">

    </div>

</form>

---

这可能与此处的代码无关。说到电子邮件，你要面对的是很多不同的系统，它们可能会带来延迟，当我在gmail inboxIn G Suite ToolBox MessageHeader上发送邮件时，会显示我的托管服务器立即发送邮件，但谷歌服务器会延迟4分钟，当你无法控制时。不幸的是，对于电子邮件，“立即”并不是一个可靠的时间表。会有延迟，你们很少能控制。也许问题出在标题上？