If you can't use Composer to install PHPMailer, you can still utilize this popular tool for sending emails in PHP through SMTP. This guide will show you how to set up PHPMailer and use it without Composer.

Step 1: Download PHPMailer

1. Go to the official PHPMailer GitHub page: PHPMailer GitHub.

2. Download the latest version of PHPMailer by clicking on "Clone or download" and choosing "Download ZIP".

3. Unzip the downloaded file into your project directory.

Step 2: Configuring PHPMailer to Use SMTP

After downloading and unzipping PHPMailer, you can start configuring it to send emails using SMTP. Here is an example of what your PHP script might look like:

<?php
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

require 'path/to/PHPMailer/src/Exception.php';
require 'path/to/PHPMailer/src/PHPMailer.php';
require 'path/to/PHPMailer/src/SMTP.php';

$mail = new PHPMailer(true);

try {
    //Server settings
    $mail->isSMTP();                                            // Send using SMTP
    $mail->Host       = 'smtp.example.com';                     // Set the SMTP server to send through
    $mail->SMTPAuth   = true;                                   // Enable SMTP authentication
    $mail->Username   = This email address is being protected from spambots. You need JavaScript enabled to view it.';               // SMTP username
    $mail->Password   = 'your_password';                        // SMTP password
    $mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;         // Enable TLS encryption
    $mail->Port       = 587;                                    // TCP port to connect to

    //Recipients
    $mail->setFrom(This email address is being protected from spambots. You need JavaScript enabled to view it.', 'Mailer');
    $mail->addAddress(This email address is being protected from spambots. You need JavaScript enabled to view it.', 'Joe User');     // Add a recipient

    // Content
    $mail->isHTML(true);                                        // Set email format to HTML
    $mail->Subject = 'Here is the subject';
    $mail->Body   

Step 3: Security Considerations

Even with a manual installation of PHPMailer, it's important to adhere to security standards:

1. Use a secure connection: Remember to use encryption (TLS or SSL) to secure your email transactions.

2. Securely store login credentials: Sensitive information like passwords and usernames should be stored securely, away from the source code.

3. Handle errors and exceptions properly: Proper error handling will help you better manage potential issues related to sending emails.

Step 4: Testing

Before deploying to production, it's important to conduct thorough testing. Ensure that your emails are correctly being delivered.

PHPMailer is a flexible and powerful tool for sending emails in PHP. Even if you can't use Composer, manually installing and configuring PHPMailer to work with SMTP is straightforward and effective. This approach allows you to take full advantage of PHPMailer for your projects.