PHPMailer is definitely a great solution to use when you want to send email using PHP. Download the PHP package from https://github.com/PHPMailer/PHPMailer.Extract the zip, and then move the extracted zip to your PHP web server.

To send an email with no authentication and no encryption.

<?php
   require "PHPMailerAutoload.php";
   $mail = new PHPMailer;
   $mail->isMail();
   $mail->Host = "mx1.example.com";
   $mail->Port = 25;
   
   $mail->setFrom("webmaster@example.com", "Webmaster");
   $mail->addAddress("John.Doe@example.com", "John Doe");
   $mail->addReplyTo("no-reply@example.com", "No Reply");

   $mail->Subject = "Here is the subject";
   $mail->Body    = "This is the message body";

   if(!$mail->send()) 
   {
       echo "Message could not be sent.";
       echo "Mailer Error: " . $mail->ErrorInfo;
   }
   else 
   {
       echo "Message has been sent";
   }
?>

To send an email with authentication and encryption.

<?php
   require "PHPMailerAutoload.php";
   $mail = new PHPMailer;
   $mail->isSMTP();
   $mail->Host = "mx1.example.com";
   $mail->SMTPAuth = true;
   $mail->Username = "user1";
   $mail->Password = "Password123";
   $mail->SMTPSecure = "tls";
   $mail->Port = 587;
   
   $mail->setFrom("webmaster@example.com", "Webmaster");
   $mail->addAddress("John.Doe@example.com", "John Doe");
   $mail->addReplyTo("no-reply@example.com", "No Reply");

   $mail->Subject = "Here is the subject";
   $mail->Body    = "This is the message body";

   if(!$mail->send()) 
   {
       echo "Message could not be sent.";
       echo "Mailer Error: " . $mail->ErrorInfo;
   }
   else 
   {
       echo "Message has been sent";
   }
?>

Debugging

If you run into problems, add the following to display verbose information.

$mail->SMTPDebug = 4;

Linux

If HTTPD is your web server, ensure HTTPD is configured to send email and network connect.

[root@server1 ~]# setsebool -P httpd_can_sendmail 1
[root@server1 ~]# setsebool -P httpd_can_network_connect 1

Verify both options are now on.

[root@server1 ~]# getsebool httpd_can_sendmail
httpd_can_sendmail --> on

[root@server1 ~]# getsebool httpd_can_network_connect
httpd_can_network_connect --> on

It's important to recognize that the PHP web server will be sending the email to the Email server. 

If a Linux web server is being used, such as Apache, HTTPD, or NGINX, the web server's SELinux context will need to allow PHP to send an email to the Email server.