$email = 'user@example.com';
if (!eregi("^[_\.0-9a-z-]+@([0-9a-z][0-9a-z-]+\.)+[a-z]{2,3}$", $email)) {
    print_error("Your email address is invalid!");
}

<?php
 
/****************************************************
*
* File:     class.email.php
* Purpose:  Email Class
* Author:   Matt West, http://mattdanger.net
* Date:     January 25, 2007
*
****************************************************/
 
class Email {
 
    // Public variables
    public $recipient;
    public $sender;
    public $reply_to;
    public $subject;
    public $body;
    public $cc;
    public $bcc;
    public $headers;
 
    /**
     * Constructor: Read in $file.
     * @param string $to        Recipient
     * @param array $from       "Sender's Name" => "Sender's Email"
     * @param string $subject   Email subject
     * @param string $body      Email body
     */
    public function __construct ($to, $from = array(), $subject, $body) {
 
        // Set receiver
        $this->receiver($to);
 
        // Set sender
        if ( !empty($from) ) {
 
            $this->sender = array( key($from) => $from[ key($from) ] );
 
        } else {
 
            $this->sender = array( $_SERVER['SERVER_ADMIN'] => $_SERVER['SERVER_ADMIN'] . '@' . $_SERVER['SERVER_NAME'] );
 
        }
 
        // Set subject
        $this->subject($subject);
 
        // Set body
        $this->body($body);
 
    }
 
    /**
     * receiver(): Set receiver of the email
     * @param array $send_to List of Names & Email addresses
     */
    public function receiver ($send_to) {
 
        foreach ($send_to as $name => $email) {
 
            if ( $this->email_is_valid($email) ) {
 
                if ( !is_numeric($name) ) { 
 
                    $this->recipient = ucfirst($name) . ' <' . $email . '>';
 
                } else {
 
                    $this->recipient = $email;
 
                }
 
                $this->recipient .= ', ';
 
            } else { 
 
                exit( $email . " is not a valid email address." ); 
 
            }
 
        }
 
        $this->recipient = preg_replace('/, $/', '', $this->recipient);
 
    }
 
    /**
     * sender(): Set send of the email
     * @param array $sender Name & Email address
     */
    public function sender ($sender) {
 
        if ( email_is_valid($sender[0]) ) {
 
            if ( !is_numeric( key($sender) ) ) { 
 
                $this->sender = ucfirst( key($sender) ) . ' <' . $email . '>';
 
            } else {
 
                $this->sender = $sender[0];
 
            }
 
        } else {
 
            exit( $sender[0] . " is not a valid email address." ); 
 
        }
 
    }
 
    /**
     * reply_to(): Set send of the email
     * @param array $reply_to Name & Email address
     */
    public function reply_to ($reply_to) {
 
        if ( email_is_valid($reply_to[0]) ) {
 
            if ( !is_numeric( key($reply_to) ) ) { 
 
                $this->reply_to = ucfirst( key($reply_to) ) . ' <' . $email . '>';
 
            } else {
 
                $this->reply_to = $sender[ key($reply_to) ];
 
            }
 
        } else {
 
            exit( $reply_to[0] . " is not a valid email address." ); 
 
        }
 
    }
 
    /**
     * cc(): Set Cc of the email
     * @param array $cc List of Names & Email addresses
     */
    public function cc ($cc) {
 
        foreach ($cc as $name => $email) {
 
            if ( email_is_valid($email) ) {
 
                if ( !is_numeric($name) ) { 
 
                    $this->cc = ucfirst($name) . ' <' . $email . '>';
 
                } else {
 
                    $this->cc = $email;
 
                }
 
                $this->cc .= ', ';
 
            } else { 
 
                exit( $email . " is not a valid email address." ); 
 
            }
 
        }
 
        $this->cc = preg_replace('/, $/', '', $this->to);
 
    }
 
    /**
     * bcc(): Set Bcc of the email
     * @param array $bcc List of Names & Email addresses
     */
    public function bcc ($bcc) {
 
        foreach ($bcc as $name => $email) {
 
            if ( !is_numeric($name) ) { 
 
                $this->bcc = ucfirst($name) . ' <' . $email . '>';
 
            } else {
 
                $this->bcc = $email;
 
            }
 
            $this->bcc .= ', ';
 
        }
 
        $this->bcc = preg_replace('/, $/', '', $this->to);
 
    }
 
    /**
     * set_headers(): Set email headers
     */
    public function set_headers () {
 
        $this->set_from();
 
        $this->headers  = "MIME-Version: 1.0rn"
                        . "From: ". $this->sender . "rn"
                        . "To: " . $this->recipient . "rn";
 
        if ( !empty($this->reply_to) ) $this->headers .= "Reply-To: " . $this->reply_to . "rn";
        if ( !empty($this->cc) ) $this->headers .= "Cc: " . $this->cc . "rn"; 
        if ( !empty($this->bcc) ) $this->headers .= "Bcc: " . $this->bcc . "rn"; 
 
        $this->headers .= "X-Priority: 1rn"
                        . "X-Mailer: PHP/" . phpversion() . "rn"
                        . "Content-type: text/html; charset=iso-8859-1rn";
 
    }
 
    /**
     * subject(): Sets the subject of the email.
     * @param string $subject The subject message.
     */
    public function subject ($subject) {
 
        // Strip any newlines
        $this->subject = str_replace('n', '', $subject);
 
    }
 
    /**
     * body(): Sets the body message of the email.
     * @param string $body The body message.
     */
    public function body ($body) {
 
        $this->body = $body;
 
    }
 
    /**
     * send(): Send the email
     * @returns boolean True if successful, false if not.
     */
    public function send () {
 
        if (mail ( $this->recipient, $this->subject, $this->body, $this->headers)) {
 
            return true;
 
        } else {
 
            return false;
 
        }
 
    }
 
    /**
     * email_is_valid():    Check whether email address is valid
     * @param string $email Email address to check
     * @returns boolean     True if address is valid, false if not.
     */
    private function email_is_valid ($email) {
 
        if (eregi("^[_.0-9a-z-]+@([0-9a-z][0-9a-z-]+.)+[a-z]{2,3}$", $email)) {
 
            return true;
 
        } else {
 
            return false;
 
        }
 
    }
 
}
 
?>