With the development of the Internet, email, as an important means of communication, has become an indispensable part of people's daily lives. Sending emails from code is a common task for web developers. PHP provides the function of sending emails via SMTP (Simple Mail Transfer Protocol), and this article will provide you with a comprehensive guide.

1. Introduction to SMTP

SMTP is a standard protocol for sending and receiving emails to servers or clients. It is a text transfer protocol. SMTP servers are usually used to send emails, while POP (Post Office Protocol) or IMAP (Internet Message Access Protocol) servers are used to receive emails.

The main function of SMTP is to attempt to deliver mail from one server to the next until the mail reaches its destination. When an SMTP client wants to send a mail, it connects to the server, sends the mail data to the server, and the server then attempts to deliver the mail to the next server until the mail reaches the recipient's SMTP server. The SMTP server uses port number 25 for communication.

2. PHP email sending function

To use SMTP to send emails in PHP, we need to use PHP’s built-in email sending function. These functions are:

1. mail() function

The simplest way to send emails in PHP is to use the mail() function. This function sends mail through the "sendmail" program in the PHP configuration. This function has the following parameters:

• $to - the recipient's email address
• $subject - the message subject
• $message - the message body
• $headers - Email headers

Sample code:

$to = "someone@example.com";
$subject = "Test mail";
$message = "Hello! This is a test email.";
$headers = "From: sender@example.com";

mail($to, $subject, $message, $headers);

2. smtp_mail() function

smtp_mail() function is a self- The defined PHP function can send emails using the SMTP protocol. This function has the following parameters:

• $to - the recipient's email address
• $subject - the message subject
• $message - the message body
• $headers - Email headers
• $smtp_username - SMTP server username
• $smtp_password - SMTP server password
• $smtp_host -SMTP server host name
• $smtp_port - SMTP server port number

Sample code:

$to = "someone@example.com";
$subject = "Test mail";
$message = "Hello! This is a test email.";
$headers = "From: sender@example.com";
$smtp_username = "smtp_username";
$smtp_password = "smtp_password";
$smtp_host = "smtp.example.com";
$smtp_port = 587;

smtp_mail($to, $subject, $message, $headers, $smtp_username, $smtp_password, $smtp_host, $smtp_port);

3. Configure SMTP server

Before using SMTP to send emails, you need to configure the SMTP server parameter. We need to know the SMTP server host name, port number, user name and password and other information.

The SMTP server host name is a domain name or IP address provided by the email service provider. The SMTP server port number is usually 25, but it can be other port numbers. If your SMTP server requires authentication, you will need to authenticate with a username and password. If authentication is not required, it can be left blank.

4. Use the PHPMailer library to send emails

PHPMailer is a popular PHP class library for sending emails. It has many advanced features such as support for SMTP authentication, attachments, HTML formatting, CC and BCC, importance and priority, etc. Here is some sample code using PHPMailer:

//引入PHPMailer庫(kù)
require_once('PHPMailer/class.phpmailer.php');

//實(shí)例化PHPMailer類
$mail = new PHPMailer();

//設(shè)置SMTP服務(wù)器
$mail->IsSMTP();
$mail->SMTPAuth = true;
$mail->SMTPSecure = 'ssl';
$mail->Host = 'smtp.example.com';
$mail->Port = 465;
$mail->Username = 'smtp_username';
$mail->Password = 'smtp_password';

//設(shè)置郵件頭信息
$mail->From = 'sender@example.com';
$mail->AddAddress('recipient@example.com');
$mail->Subject = 'Test email';
$mail->Body = 'This is a test email message.';

//發(fā)送郵件
if(!$mail->Send()) {
    echo 'Message could not be sent.';
    echo 'Mailer Error: ' . $mail->ErrorInfo;
} else {
    echo 'Message has been sent.';
}

In this code, we instantiate the PHPMailer class and set the parameters of the SMTP server. Then set the email header information and send the email by calling the Send() method.

5. Summary

This article provides you with a guide on how to send emails via SMTP using PHP. You can send emails using PHP's built-in mail() function or a custom smtp_mail() function. If you need more advanced features such as attachments, HTML formatting, SMTP authentication, CC and BCC, etc., use the PHPMailer library. No matter which method you use, you'll need to understand SMTP server setup and authentication.

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