Description:
------------
Using standard imap functions to grab and store mails, I need to keep track of the Message-ID (and References and In-Reply-To) to build threads. 
I can successfully do it with mails sent from a lot of different accounts to my email test account but every mail sent from a gmail account does not have a Message-ID when I fetched it with a php script.
I checked the same mails from my thunderbird (sent the same mail to another account and downloaded it with TB) and I verified that a Message-ID indeed exists.
It seems "References" exists and lists all "Message-ID" in the thread except the one from gmail. 

I suspect it's due to the extension (in characters) of gmail Message-ID (it always seems larger than the other ones)




Reproduce code:
---------------
$mbox = imap_open("{imap.domain:143/imap}INBOX",$user,$pass);
 if($mbox)
 {  
     $nmsg=imap_num_msg($mbox);
  for ($i=1; $i<=$nmsg; $i++) {
   $header = imap_header($mbox, $i); 
   print_r($header); echo '<br><br>';
  }
 }
 else
 {
     echo 'Connection failed<br>';
 }
imap_close($mbox);
}

Expected result:
----------------
In mails sent from a gmail account I expect to get a Message-ID in the header as defined in RFC822.


Actual result:
--------------
In mails sent from gmail I get a null value in Message-ID although I know that a Message-ID exists.