如果只使用mail()函数，则需要完成配置文件。

您需要打开邮件扩展，并设置SMTP smtp_port等，最重要的是，设置您的用户名和密码。没有它，邮件就无法发送。此外，您还可以使用PHPMail类来发送。

$name = $_POST['name'];
$email = $_POST['email'];
$reciver = '/* Reciver Email address */';
if (filter_var($reciver, FILTER_VALIDATE_EMAIL)) {
    $subject = $name;
    // To send HTML mail, the Content-type header must be set.
    $headers = 'MIME-Version: 1.0' . "\r\n";
    $headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";
    $headers .= 'From:' . $email. "\r\n"; // Sender's Email
    //$headers .= 'Cc:' . $email. "\r\n"; // Carbon copy to Sender
    $template = '<div style="padding:50px; color:white;">Hello ,<br/>'
        . '<br/><br/>'
        . 'Name:' .$name.'<br/>'
        . 'Email:' .$email.'<br/>'
        . '<br/>'
        . '</div>';
    $sendmessage = "<div style=\"background-color:#7E7E7E; color:white;\">" . $template . "</div>";
    // Message lines should not exceed 70 characters (PHP rule), so wrap it.
    $sendmessage = wordwrap($sendmessage, 70);
    // Send mail by PHP Mail Function.
    mail($reciver, $subject, $sendmessage, $headers);
    echo "Your Query has been received, We will contact you soon.";
} else {
    echo "<span>* invalid email *</span>";
}

我在000webhost上做了以下工作:

$headers  = "MIME-Version: 1.0" . "\r\n";
$headers .= "Content-type: text/html; charset=iso-8859-1" . "\r\n";
$headers .= "From: ". $from. "\r\n";
$headers .= "Reply-To: ". $from. "\r\n";
$headers .= "X-Mailer: PHP/" . phpversion();
$headers .= "X-Priority: 1" . "\r\n";

发送邮件时直接输入邮箱地址:

mail('email@gmail.com', $subject, $message, $headers)

使用“and not”。

这个代码工作，但电子邮件收到了半小时的延迟。

大多数情况下，在共享主机中禁用了mail()函数。 更好的选择是使用SMTP。最好的选择是Gmail或SendGrid。

SMTPconfig.php

<?php 
    $SmtpServer="smtp.*.*";
    $SmtpPort="2525"; //default
    $SmtpUser="***";
    $SmtpPass="***";
?>

SMTPmail.php

<?php
class SMTPClient
{

    function SMTPClient ($SmtpServer, $SmtpPort, $SmtpUser, $SmtpPass, $from, $to, $subject, $body)
    {

        $this->SmtpServer = $SmtpServer;
        $this->SmtpUser = base64_encode ($SmtpUser);
        $this->SmtpPass = base64_encode ($SmtpPass);
        $this->from = $from;
        $this->to = $to;
        $this->subject = $subject;
        $this->body = $body;

        if ($SmtpPort == "") 
        {
            $this->PortSMTP = 25;
        }
        else
        {
            $this->PortSMTP = $SmtpPort;
        }
    }

    function SendMail ()
    {
        $newLine = "\r\n";
        $headers = "MIME-Version: 1.0" . $newLine;  
        $headers .= "Content-type: text/html; charset=iso-8859-1" . $newLine;  

        if ($SMTPIN = fsockopen ($this->SmtpServer, $this->PortSMTP)) 
        {
            fputs ($SMTPIN, "EHLO ".$HTTP_HOST."\r\n"); 
            $talk["hello"] = fgets ( $SMTPIN, 1024 ); 
            fputs($SMTPIN, "auth login\r\n");
            $talk["res"]=fgets($SMTPIN,1024);
            fputs($SMTPIN, $this->SmtpUser."\r\n");
            $talk["user"]=fgets($SMTPIN,1024);
            fputs($SMTPIN, $this->SmtpPass."\r\n");
            $talk["pass"]=fgets($SMTPIN,256);
            fputs ($SMTPIN, "MAIL FROM: <".$this->from.">\r\n"); 
            $talk["From"] = fgets ( $SMTPIN, 1024 ); 
            fputs ($SMTPIN, "RCPT TO: <".$this->to.">\r\n"); 
            $talk["To"] = fgets ($SMTPIN, 1024); 
            fputs($SMTPIN, "DATA\r\n");
            $talk["data"]=fgets( $SMTPIN,1024 );
            fputs($SMTPIN, "To: <".$this->to.">\r\nFrom: <".$this->from.">\r\n".$headers."\n\nSubject:".$this->subject."\r\n\r\n\r\n".$this->body."\r\n.\r\n");
            $talk["send"]=fgets($SMTPIN,256);
            //CLOSE CONNECTION AND EXIT ... 
            fputs ($SMTPIN, "QUIT\r\n"); 
            fclose($SMTPIN); 
            // 
        } 
        return $talk;
    } 
}
?>

contact_email.php

<?php 
include('SMTPconfig.php');
include('SMTPmail.php');
if($_SERVER["REQUEST_METHOD"] == "POST")
{
    $to = "";
    $from = $_POST['email'];
    $subject = "Enquiry";
    $body = $_POST['name'].'</br>'.$_POST['companyName'].'</br>'.$_POST['tel'].'</br>'.'<hr />'.$_POST['message'];
    $SMTPMail = new SMTPClient ($SmtpServer, $SmtpPort, $SmtpUser, $SmtpPass, $from, $to, $subject, $body);
    $SMTPChat = $SMTPMail->SendMail();
}
?>

总是尝试在邮件函数中发送标题。 如果您通过localhost发送邮件，则执行SMTP设置以发送邮件。 如果您通过服务器发送邮件，请检查您的服务器上是否启用了电子邮件发送功能。

对于任何发现这一点的人，我不建议使用邮件。有一些答案涉及到这个问题，但没有解释为什么会这样。

PHP's mail function is not only opaque, it fully relies on whatever MTA you use (i.e. Sendmail) to do the work. mail will only tell you if the MTA failed to accept it (i.e. Sendmail was down when you tried to send). It cannot tell you if the mail was successful because it's handed it off. As such (as John Conde's answer details), you now get to fiddle with the logs of the MTA and hope that it tells you enough about the failure to fix it. If you're on a shared host or don't have access to the MTA logs, you're out of luck. Sadly, the default for most vanilla installs for Linux handle it this way.

邮件库(PHPMailer、Zend Framework 2+等)的功能与邮件非常不同。它们直接打开接收邮件服务器的套接字，然后通过该套接字直接发送SMTP邮件命令。换句话说，类充当自己的MTA(注意，您可以告诉库使用邮件来最终发送邮件，但我强烈建议您不要这样做)。

这意味着您可以直接看到来自接收服务器的响应(例如，在PHPMailer中，您可以打开调试输出)。不用再猜测邮件是否发送失败或原因。

如果您正在使用SMTP(即您正在调用isSMTP())，您可以使用SMTPDebug属性获得SMTP对话的详细记录。 通过在脚本中包含如下一行来设置该选项: $mail->SMTPDebug = 2;

您还可以获得更好的界面。对于邮件，你必须设置所有的标题，附件等。有了库，就有了专门的函数来实现这一点。这也意味着函数正在处理所有棘手的部分(比如头文件)。