(PHP 4, PHP 5, PHP 7)

imap_8bit8 ビット文字列を quoted-printable 文字列に変換する


string imap_8bit ( string $string )

(» RFC2045, section 6.7 に基づき) 8 ビット文字列を quoted-printable 文字列に変換します。



変換する 8 ビット文字列。


quoted-printable 文字列を返します。


  • imap_qprint() - quoted-printable 文字列を 8 ビット文字列に変換する

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User Contributed Notes 16 notes

13 years ago
imap_8bit seems to have a bug as it doesn't encode "?".
Had a lot of trouble to encode a mail-subject with
german umlaute with an ending "?"...

Try this:

$subject = "=?iso-8859-1?Q?" . str_replace("?","=3F",imap_8bit($tsubject_to_encode)) . "?=";
11 years ago

I use the following function instead of imap_8bit
when using PHP without the IMAP module,
which is based on code found in,
and giving (supposedly) exactly the same results as imap_8bit,
(tested on thousands of random strings containing lots
of spaces, tabs, crlf, lfcr, lf, cr and so on,
no counterexample found SO FAR:)

AND you can force a trailing space to be encoded,
as opposed to what imap_8bit does,
which I consider is a violation of RFC2045,
by commenting that one central line.

function quoted_printable_encode($sText,$bEmulate_imap_8bit=true) {
// split text into lines

  for (
$i=0;$i<count($aLines);$i++) {
$sLine =& $aLines[$i];
    if (
strlen($sLine)===0) continue; // do nothing, if empty

$sRegExp = '/[^\x09\x20\x21-\x3C\x3E-\x7E]/e';

// imap_8bit encodes x09 everywhere, not only at lineends,
    // for EBCDIC safeness encode !"#$@[\]^`{|}~,
    // for complete safeness encode every character :)
if ($bEmulate_imap_8bit)
$sRegExp = '/[^\x20\x21-\x3C\x3E-\x7E]/e';

$sReplmt = 'sprintf( "=%02X", ord ( "$0" ) ) ;';
$sLine = preg_replace( $sRegExp, $sReplmt, $sLine ); 

// encode x09,x20 at lineends
$iLength = strlen($sLine);
$iLastChar = ord($sLine{$iLength-1});

//              !!!!!!!!   
      // imap_8_bit does not encode x20 at the very end of a text,
      // here is, where I don't agree with imap_8_bit,
      // please correct me, if I'm wrong,
      // or comment next line for RFC2045 conformance, if you like
if (!($bEmulate_imap_8bit && ($i==count($aLines)-1)))
      if ((
$iLastChar==0x09)||($iLastChar==0x20)) {
$sLine .= ($iLastChar==0x09)?'09':'20';
// imap_8bit encodes x20 before chr(13), too
    // although IMHO not requested by RFC2045, why not do it safer :)
    // and why not encode any x20 around chr(10) or chr(13)
if ($bEmulate_imap_8bit) {
$sLine=str_replace(' =0D','=20=0D',$sLine);
//$sLine=str_replace(' =0A','=20=0A',$sLine);
      //$sLine=str_replace('=0D ','=0D=20',$sLine);
      //$sLine=str_replace('=0A ','=0A=20',$sLine);

// finally split into softlines no longer than 76 chars,
    // for even more safeness one could encode x09,x20
    // at the very first character of the line
    // and after soft linebreaks, as well,
    // but this wouldn't be caught by such an easy RegExp                  
preg_match_all( '/.{1,73}([^=]{0,2})?/', $sLine, $aMatch );
$sLine = implode( '=' . chr(13).chr(10), $aMatch[0] ); // add soft crlf's

// join lines into text
return implode(chr(13).chr(10),$aLines);
k dot kozlowski at enter dot pl
12 years ago
I had problems with encoding large subjects with polish characters. The problem was that imap_8bit() splits subject (on 75-th char) but when I add "=?ISO-8859-2?Q?" the header is too long.

This is a solution :
= str_replace(" ", "_", trim($subject)) ;
// We need to delete "=\r\n" produced by imap_8bit() and replace '?'
$subject = str_replace("?", "=3F", str_replace("=\r\n", "", imap_8bit($subject))) ;
// Now we split by \r\n but with encoding text "=?ISO ..."
$subject = str_replace("\r\n", "?=\r\n =?ISO-8859-2?Q?", chunk_split($subject, 55)) ;
// We also have to remove last unneeded encoding text :
$subject = "=?ISO-8859-2?Q?" . substr($subject, 0, strlen($subject)-20) . "?=" ;
roman at REMOVETHIS dot teamnet dot com dot pl
10 years ago
Code based on k dot kozlowski at enter dot pl but for UTF-8
(the only problem i encounter is SUBJECT_ENCODED_TWICE on SPAM test with very long subject, but the same produce others MUA's)
function header_quoted_printable_encode($string, $encoding='UTF-8') {
    $string = str_replace(" ", "_", trim($string)) ;
    // We need to delete "=\r\n" produced by imap_8bit() and replace '?'
    $string = str_replace("?", "=3F", str_replace("=\r\n", "", imap_8bit($string))) ;
    // Now we split by \r\n - i'm not sure about how many chars (header name counts or not?)
    $string = chunk_split($string, 73);
    // We also have to remove last unneeded \r\n :
    $string = substr($string, 0, strlen($string)-2);
    // replace newlines with encoding text "=?UTF ..."
    $string = str_replace("\r\n", "?=".HEAD_CRLF." =?".$encoding."?Q?", $string) ;
    return '=?'.$encoding.'?Q?'.$string.'?=';
Michael Konecny
6 years ago
There is a bug in MS Exchange server, that improperly handles CRLFs. Seems like it converts both CR and LF into LF, so, instead of getting just a new line, you get TWO new lines.
The header information is then improperly parsed by the e-mail client, and is usually viewed in the message body.

This can make custom-created headers unusable.

The only way I found to get around this is to go against RFC rules for header formatting, and use only \n for new lines.

Unfortunately I haven't been able to learn the version of Exchange server where this happened, but I have the feeling that it's not just the one I was unlucky to encounter.

Hope this helps someone.
hans at lintoo dot dk
12 years ago
I modified nick at plumdigitalmedia dot com's note so that it may support ISO-8859-1 encoded headers:
public function encodeSubject($string,$prefix="=?ISO-8859-1?Q?",$postfix="?=")    {
$crlf    = "\n\t";
$string  = preg_replace('!(\r\n|\r|\n)!', $crlf, $string) . $crlf ;
$f[]    = '/([\000-\010\013\014\016-\037\075\177-\377])/e' ;
$r[]    = "'=' . sprintf('%02X', ord('\\1'))" ;
$f[]    = '/([\011\040])' . $crlf . '/e' ;
$r[]    = "'=' . sprintf('%02X', ord('\\1')) . '" . $crlf . "'" ;
$string  = preg_replace($f, $r, $string);
$prefix.trim(wordwrap($string, 70 - strlen($prefix) - strlen($postfix), ' ' . $postfix . $crlf . $prefix, true)).$postfix;
Regards, Hans @
9 years ago
umu's code seems to work great. BUT if you are on a Unix system you should replace all chr(13).chr(10) with just chr(10)

Works for me anyway on php5.mail() -> qmail@suse10.1 -> outlook express
zuffa at isdd dot sk
17 years ago
Warning !
This function splits input text into
several lines aligned to 75 characters.
This is critical when you need input
text to be only one striaght line as
e.g. in e-mail header values.
esh dot software at energiash dot com
8 years ago
When producing quoted printable emails this is the right way

$subject="Subject: =?iso-8859-1?Q?". imap_8bit("áéíóú"). "?=";

and the following would do the wrong thing, because qprint over "=ED" would produce 8bit data ( í ):

$subject="Subject: =?iso-8859-1?Q?". imap_qprint("=ED"). "?=";
nick at plumdigitalmedia dot com
12 years ago
This function appears to wrap lines in the middle of words, not just at whitespace, which upsets some versions of Outlook Express when used to format email body text. We've had more luck with this function:


    function quoted_printable($string)
        $crlf    = "\n" ;
        $string  = preg_replace('!(\r\n|\r|\n)!', $crlf, $string) . $crlf ;
        $f[]     = '/([\000-\010\013\014\016-\037\075\177-\377])/e' ;
        $r[]     = "'=' . sprintf('%02X', ord('\\1'))" ;
        $f[]     = '/([\011\040])' . $crlf . '/e' ;
        $r[]     = "'=' . sprintf('%02X', ord('\\1')) . '" . $crlf . "'" ;
        $string  = preg_replace($f, $r, $string) ;
        return trim(wordwrap($string, 70, ' =' . $crlf)) ;

MagicalTux at FF.ST
13 years ago
Reading Bully's note :
you can use the following to make a larger subject:
$encoded = str_replace("=\r\n","",imap_8bit($string_to_encode));
It's wrong. The header MAY NOT go over 75 chars per line.

The right solution :
$encoded = rtrim( str_replace( "\n","\n\t", imap_8bit ($string_to_encode)))."\r\n";

It will add \t at the start of the encoded new lines.
Mailers to see the lines after Subject: as extensions of this header.
dave at jufer dot info
2 years ago
Encode a mail-subject-string to a encoded-word according to RFC2047 with awareness of special characters and total-linelength of 75.
Example: "Subject Testä" -> "=?ISO-8859-1?Q?Subject_Test=E4?="
function getSubjectEncoded($_str,$_charset='ISO-8859-1'){
// 27.08.2015 david jufer
    // Convert an 8bit string to a encoded-word string (according to RFC2047)
    // encoded-word = "=?" charset "?" encoding "?" encoded-text "?="
    // An 'encoded-word' may not be more than 75 characters long, including 'charset', 'encoding', 'encoded-text', and delimiters.
    // The "Q" encoding is similar to the "Quoted-Printable" content-transfer-encoding defined in RFC 2045
$ret = '';
$str = imap_8bit($_str);
$len = 7+strlen($_charset);
// remove linebreaks from imap_8bit, string chunks are too long
$str = str_replace("=\r\n",'',$str);
// insert linebreaks at right position, be aware of special chars ("ä" "=E4") do not split them
$s = 0;
$l = 75-$len;
$ts = $s;
$s += $l-2;
        }else if(
$s += $l-1;
$s += $l;
$ret .= "\r\n".substr($str,$ts,$s-$ts);
// remove first linebreak, replace SPACES with "_"
$ret = str_replace(' ','_',trim($ret));
// put together encoded-word
$ret = '=?'.$_charset.'?Q?'.str_replace("\r\n","?=\r\n =?".$_charset."?Q?",$ret)."?=";
// rückgabe
return $ret;
marco dot manngatter at ecg-leipzig dot de
12 years ago
you can use the following to make a larger subject.
use the imap_qprint() function, to convert your subject.


.= "=?iso-8859-1?Q?" . imap_qprint($subject) . "?=";

php dot net at werner-ott dot de
14 years ago
A comment on the "split-after-75-characters" phenomenon:

By splitting lines up after 75 characters, the function's behaviour is complying to RFC2047 ( (which specifies a protocol for the representation of non-ASCII text in message headers), section "2. Syntax of encoded-words".

A so called 'encoded word' has the following format:

   encoded-word = "=?" charset "?" encoding "?" encoded-text "?="

An 'encoded-word' may not be more than 75 characters long, including 'charset', 'encoding', 'encoded-text', and delimiters.  If it is desirable to encode more text than will fit in an 'encoded-word' of 75 characters, multiple 'encoded-word's (separated by CRLF SPACE) may be used.

bully at newearth dot de
15 years ago
you can use the following to make a larger subject:

$encoded = str_replace("=\r\n","",imap_8bit($string_to_encode));
hans at lintoo dot dk
11 years ago
The code below this note gives a lot of trouple with SpamAssasin, to fix it you will need to encode your subject with something like this:
* Function to encode a header if necessary
* according to RFC2047
private function encodeHeader($input, $charset = 'ISO-8859-1')
preg_match_all('/(\s?\w*[\x80-\xFF]+\w*\s?)/', $input, $matches);
    foreach (
$matches[1] as $value) {
$replacement = preg_replace('/([\x20\x80-\xFF])/e', '"=" . strtoupper(dechex(ord("\1")))', $value);
$input = str_replace($value, '=?' . $charset . '?Q?' . $replacement . '?=', $input);
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