<!-- Collection of code snippets by Arne Vajhøj -->
<!-- posted to eksperten.dk, usenet and other places (2002-now) -->
<?php

class SmartMailer {
    // content types
    const TYPE_UNKNOWN = 100;
    const TYPE_TEXT = 101;
    const TYPE_HTML = 102;
    // character sets
    const CS_UNKNOWN = 200;
    const CS_USASCII = 201;
    const CS_ISO88591 = 202;
    const CS_UTF8 = 203;
    // default character set if 8 bit and not possible to guess
    private $default_cs;
    // constructor
    public function __construct() {
        $this->default_cs = SmartMailer::CS_UTF8;
    }
    // access default charcter set
    public function get_default_cs() {
        return $this->default_cs;
    }
    public function set_default_cs($cs) {
        cs_type_to_string($cs); // will throw exception if unknown character set
        $this->default_cs = $cs;
    }
    // convert content type code to actual content type string
    private function type_code_to_string($type) {
        switch ($type) {
            case SmartMailer::TYPE_TEXT:
                return "text/plain";
            case SmartMailer::TYPE_HTML:
                return "text/html";
            default:
                throw new Exception('Unsupported content type code ' . $type);
        }
    }
    // convert character set code to actual character set string
    private function cs_code_to_string($cs) {
        switch ($cs) {
            case SmartMailer::CS_USASCII:
                return "US-ASCII";
            case SmartMailer::CS_ISO88591:
                return "ISO-8859-1";
            case SmartMailer::UTF8:
                return "UTF-8";
            default:
                throw new Exception('Unsupported character set code ' . $cs);
        }
    }
    // attempt to guess content type
    private function guess_type($s) {
        $res = preg_match('#<(\w+).+</(\w+)#', $s, $matches);
        return ($res && ($matches[1] == $matches[2])) ? SmartMailer::TYPE_HTML : SmartMailer::TYPE_TEXT;
    }
    // attempt to guess character set
    private function guess_cs($s) {
        $s8bit = array_filter(str_split($s), function($c) { return ord($c) >= 128; });
        if(count($s8bit) == 0) return SmartMailer::CS_USASCII;
        $s8bitnbsp = array_filter($s8bit, function($c) { return ord($c) == 0xA0; });
        $s8bitlatin = array_filter($s8bit, function($c) { return ord($c) >= 0xC0; });
        if(count($s8bitnbsp) == 0 && count($s8bitlatin) > 0) {
            return SmartMailer::CS_ISO88591;
        } else if(count($s8bitnbsp) > 0) {
            return SmartMailer::CS_UTF8;
        } else {
            return $this->default_cs;
        }
    }
    // header encode
    private function header_encode($hdr) {
        $hdrcs = $this->guess_cs($hdr);
        if($hdrcs == SmartMailer::CS_USASCII) {
            return $hdr;
        } else {
            return '=?' . $this->cs_code_to_string($hdrcs) . '?Q?' . quoted_printable_encode($hdr) . '?=';
        }
    }
    // email address encode
    private function email_address_encode($addr) {
        $addrparts = explode(' <', $addr);
        if(count($addrparts) == 2) {
            return $this->header_encode($addrparts[0]) . ' <' . $addrparts[1];
        } else {
            return $addr;
        }
    }
    // actual send
    public function send_email($from, $to, $subject, $body, $type = SmartMailer::TYPE_UNKNOWN, $cs = SmartMailer::CS_UNKNOWN) {
        $from = $this->email_address_encode($from);
        $to = $this->email_address_encode($to);
        $subject = $this->header_encode($subject);
        $type = ($type == SmartMailer::TYPE_UNKNOWN) ? $this->guess_type($body) : $type;
        $bodycs = ($cs == SmartMailer::CS_UNKNOWN) ? $this->guess_cs($body) : $cs;
        $contenttype = $this->type_code_to_string($type) . '; charset=' . $this->cs_code_to_string($bodycs);
        if($bodycs == SmartMailer::CS_USASCII) {
            $contentencoding = '7bit';
        } else {
            $contentencoding = 'quoted-printable';
            $body = quoted_printable_encode($body);
        }
        $headers = "From: $from\r\n" .
                   "Content-Type: $contenttype\r\n" .
                   "MIME-Version: 1.0\r\n" .
                   "Content-Transfer-Encoding: $contentencoding";
        mail($to, $subject, $body, $headers);
    }                   
}

?>