Simple and intuitive email class (using the native mail function from PHP)

index.php

<?php
require 'mailer.php';

$message = <<<MSG
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
MSG;

// Creates a new mailer instance and enable mail greeting
$mailer = new Mailer(true);

// Adds a new recipient (receiver)
$mailer->addRecipient('miranda@lunnaly.com', 'All Unser Miranda');

// Sets the message to send
$mailer->setMessage($message);

// Sets the email subject
$mailer->setSubject('Lorem Ipsum');

// Sets the email sender
$mailer->setFrom('John Doe', 'johndoe@example.com');

// Specify the email content type ('html' or 'plain')
$mailer->is('plain');

// Send the emails :-)
if ($mailer->send()) {
    echo "Far out! The email has been sent! :-)"
} else {
    echo "Bad lucky! The email wasn't sent! :-(";
}
?>

mailer.php

<?php
/**
 * Mailer class wrapper
 *
 * @package     Mailer
 * @author      Miranda <miranda@lunnaly.com>
 * @license     http://www.opensource.org/licenses/mit-license.php MIT License
 * @link        http://lunnaly.com
 * @version     0.1.0
 */
class Mailer {
    /**
     * Email recipients
     *
     * @access  protected
     * @var     array
     */
    protected $recipients = array();

    /**
     * Email boundary
     *
     * @access  protected
     * @var     int
     */
    protected $bound = null;

    /**
     * Email content
     *
     * @access  protected
     * @var     string
     */
    protected $message = null;

    /**
     * Email subject
     *
     * @access  protected
     * @var     string
     */
    protected $subject = null;

    /**
     * Email sender (author)
     *
     * @access  protected
     * @var     string
     */
    protected $fromAddr = null;

    /**
     * Add a greeting message at top of the email
     *
     * @access  protected
     * @var     bool
     */
    protected $addGreeting = false;

    /**
     * Email content type (such as: html or plain text).
     *
     * @access  protected
     * @var     bool
     */
    protected $type = true;

    /**
     * Email importance level
     *
     * @access  protected
     * @var     string
     */
    protected $level = null;

    /**
     * Email attachments
     *
     * @access  protected
     * @var     array
     */
    protected $attachments = array();

    /**
     * Constructor of this class
     *
     * @access  public
     * @param   bool $greeting
     */
    public function __construct($greeting = false) {
        $this->addGreeting = $greeting;
        $this->bound = uniqid(time());
        $this->level = 'normal';
    }

    /**
     * Add an email recipient to send for.
     *
     * @access  public
     * @param   string $email
     * @param   string $name
     * @return  object
     */
    public function addRecipient($email, $name = null) {
        if (!isset($email)) {
            throw new MailerException('Please specify an email!');
        }

        if (isset($name) && !empty($name)) {
            $this->recipients[$name] = $email;
        } else {
            $this->recipits[] = $email;
        }

        return $this;
    }

    /**
     * Set the email content to send.
     *
     * @access  public
     * @param   string $msg
     * @return  object
     */
    public function setMessage($msg) {
        if (!isset($msg)) {
            throw new MailerException('You must specify a message to send, dear padawan!');
        }

        $this->message = (isset($msg) && !empty($msg)) ? trim(stripslashes($msg)) : null;

        return $this;
    }

    /**
     * Set the email subject
     *
     * @access  public
     * @param   string $subject
     * @return  object
     */
    public function setSubject($subject) {
        if (!isset($subject)) {
            throw new MailerException('Wait a minute, a subject is required luke!');
        }

        $this->subject = (isset($subject) && !empty($subject)) ? $subject : null;

        return $this;
    }

    /**
     * Set the email sender
     *
     * @access  public
     * @param   string $name
     * @param   string $email
     * @return  object
     */
    public function setFrom($name, $email) {
        if (!isset($name) || !isset($email)) {
            throw new MailerException('Unless the email/name is from your sister, you must enter an email or a name!');
        }

        $this->fromAddr = (isset($name, $email) && (!empty($name)) && !empty($email)) ? $name . " <" . $email . ">": null;

        return $this;
    }

    /**
     * Set the email importance level
     *
     * @access  public
     * @param   string $lvl
     * @return  object
     */
    public function setLevel($lvl = 'normal') {
        $this->level = (isset($lvl) && !empty($lvl)) ? $lvl : null;

        return $this;
    }

    /**
     * Add an attachment to send via Email
     *
     * @access  public
     * @param   string $file
     * @return  object
     */
    public function attachment($file) {
        if (!file_exists($file)) {
            throw new MailerException('Provided file (' . $file . ') to add as attachments doesn\' exists!');
        }

        $base = basename($file);
        $header =  "--{$this->bound}\r\n";
        $header .= "Content-Type: ". File::mime($file, true) ."; name=\"{$base}\"\r\n";
        $header .= "Content-Transfer-Encoding: base64\r\n";
        $header .= "Content-Disposition: attachment; filename=\"{$base}\"\r\n\r\n";
        $header .= chunk_split(base64_encode(fread(fopen($file, 'rb'), filesize($file))), 72) . "\r\n";

        $this->attachments[] = $header;

        return $this;
    }

    /**
     * Set the email content type
     *
     * @access  public
     * @param   string $type
     * @return  object
     */
    public function is($type) {
        if (!isset($type)) {
            throw new MailerException('Luke, i\'m your father and you must specify the email type!');
        }

        $this->type = (isset($type) && !empty($type)) ? $type : null;

        return $this;
    }

    /**
     * Send email to $this->recipients
     *
     * @access  public
     * @param   int $pauseEvery
     * @return  bool
     */
    public function send($pauseEvery = 25) {
        $count = 1;

        foreach ($this->recipients as $toName => $toAddr) {
            // Increments the counter
            $count++;

            // Every $pauseEvery emails, wait for three seconds
            if (is_int($pauseEvery) && ($count % $pauseEvery) == 0) {
                sleep(3);
            }

            // Now send the email
            if ($this->sendEmail($toAddr, $toName)) {
                // Increment counter
                $count++;

                // Continue
                continue;
            } else {
                return false;
            }
        }

        return true;
    }

    /**
     * Send email to the specified address with a greeting with the $toName if greeting is enabled
     *
     * @access  private
     * @param   string $toAddr
     * @param   string $toName
     * @return  void
     */
    private function sendEmail($toAddr, $toName = null) {
        if (!isset($toAddr)) {
            throw new MailerException('Can you please specify an email address C-3PO?');
        }

        // Prepare name and subject
        $toName  = (isset($toName) && is_string($toName))  ? $toName  : 'Sir/Madam';

        // Lunnaly version
        $version = phpversion();

        // Compose body
        $body = ($this->addGreeting === true) ? "Dear, " . $toName . "\r\n" . $this->message : $this->message;

        // Set headers
        $headers = "X-Mailer: PHP v{$version}\r\n";
        $headers .= 'From: ' . $this->fromAddr . "\r\n";
        $headers .= 'To: ' . $toName . " <{$toAddr}>\r\n";
        $headers .= $this->buildHeaders($body);

        if (count($this->attachments) > 0) {
            $headers .= $this->attachments;
        }

        // Send the email
        if (mail($toAddr, $this->subject, $body, $headers)) {
            return true;
        }

        return false;
    }

    /**
     * Build some needed custom headers
     *
     * @access  private
     * @param   string $content
     * @return  string
     */
    private function buildHeaders($content) {
        if (!isset($content)) {
            throw new MailerException('The email body is more empty than the Death Star after exploding...');
        }

        // Custom headers based on the current timestamp
        $headers = "Date: " . Date::today('r') . "\r\n";
        $headers .= "MIME-Version: 1.0\r\n";
        $headers .= "Content-Type: multipart/alternative; boundary=\"{$this->bound}\"\r\n\r\n";
        $headers .= "--{$this->bound}\r\n";

        // Email importance level
        $headers .= "Importance: {$this->level}\r\n";

        switch ($this->type) {
            case 'html':
                $headers .= "Content-Transfer-Encoding: quoted-printable\r\n";
                $headers .= "Content-Type:text/html;charset=" . String::encoding() . "\r\n";
                $headers .= "<html>\n<body>\n{$content}\n</body>\n</html>\r\n\r\n";
                $headers .= "--{$this->bound}\r\n\r\n";
                break;
            case 'plain':
            default:
                $headers .= "Content-Transfer-Encoding: quoted-printable\r\n";
                $headers .= "Content-Type:text/plain;charset=" . String::encoding() . "\r\n";
                $headers .= "{$content}\r\n\r\n";
                $headers .= "--{$this->bound}\r\n\r\n";
                break;
        }

        return $headers;
    }
}

final class MailerException extends RuntimeException {}
?>