PHP IMAP decoding messages

imap_bodystruct() or imap_fetchstructure() should return this info to you. The following code should do exactly what you're looking for:

<?php
$hostname = '{********:993/imap/ssl}INBOX';
$username = '*********';
$password = '******';

$inbox = imap_open($hostname,$username,$password) or die('Cannot connect to server: ' . imap_last_error());

$emails = imap_search($inbox,'ALL');

if($emails) {
    $output = '';
    rsort($emails);

    foreach($emails as $email_number) {
        $overview = imap_fetch_overview($inbox,$email_number,0);
        $structure = imap_fetchstructure($inbox, $email_number);

        if(isset($structure->parts) && is_array($structure->parts) && isset($structure->parts[1])) {
            $part = $structure->parts[1];
            $message = imap_fetchbody($inbox,$email_number,2);

            if($part->encoding == 3) {
                $message = imap_base64($message);
            } else if($part->encoding == 1) {
                $message = imap_8bit($message);
            } else {
                $message = imap_qprint($message);
            }
        }

        $output.= '<div class="toggle'.($overview[0]->seen ? 'read' : 'unread').'">';
        $output.= '<span class="from">From: '.utf8_decode(imap_utf8($overview[0]->from)).'</span>';
        $output.= '<span class="date">on '.utf8_decode(imap_utf8($overview[0]->date)).'</span>';
        $output.= '<br /><span class="subject">Subject('.$part->encoding.'): '.utf8_decode(imap_utf8($overview[0]->subject)).'</span> ';
        $output.= '</div>';

        $output.= '<div class="body">'.$message.'</div><hr />';
    }

    echo $output;
}

imap_close($inbox);
?>

Returned Objects for imap_fetchstructure()

1. encoding (Body transfer encoding)

Transfer encodings (may vary with used library)

0 7BIT 1 8BIT 2 BINARY 3 BASE64 4 QUOTED-PRINTABLE 5 OTHER

$s = imap_fetchstructure($mbox,$mid);
if ($s->encoding==3)
    $data = base64_decode($data);

You can look at this example.

Imap/Imap

Here's code snippet

switch ($encoding) {
    # 7BIT
    case 0:
        return $text;
    # 8BIT
    case 1:
        return quoted_printable_decode(imap_8bit($text));
    # BINARY
    case 2:
        return imap_binary($text);
    # BASE64
    case 3:
        return imap_base64($text);
    # QUOTED-PRINTABLE
    case 4:
        return quoted_printable_decode($text);
    # OTHER
    case 5:
        return $text;
    # UNKNOWN
    default:
        return $text;
}