imap_thread
    (PHP 4 >= 4.1.0, PHP 5)
imap_thread -- 
     Returns a tree of threaded message
    
Description
array 
imap_thread ( resource stream_id [, int options] )
     imap_thread() returns an associative array containing
     a tree of messages threaded by REFERENCES, or FALSE
     on error.
    
     Every message in the current mailbox will be represented by three entries
     in the resulting array:
     
    
     
Example 1. imap_thread() Example 
<?php
  // Here we're outputting the threads of a newsgroup, in HTML
  $nntp = imap_open('{news.example.com:119/nntp}some.newsgroup', '', ''); $threads = imap_thread($nntp);
  foreach ($threads as $key => $val) {   $tree = explode('.', $key);   if ($tree[1] == 'num') {     $header = imap_headerinfo($nntp, $val);     echo "<ul>\n\t<li>" . $header->fromaddress . "\n";   } elseif ($tree[1] == 'branch') {     echo "\t</li>\n</ul>\n";   } }
  imap_close($nntp);
  ?>
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