Missing mails in Exchange 2007

Hi all

I have a mailserver with Exchange 2007. On the LAN i have a Windows 2003 server sending mails to local users.  Normally this works fine.  No antispam installed
Running this below results : Only mail 2 and 3 are being received ?

$content = "Tjek din opgave";                
$send_mail = mail($email, $subj, $content, $fra);                
             
$content2 = "Test paa email som kun fjk skulle faa...";
$send_mail2 = mail($email, $subj, $content2, $fra);

$content3 = "Tjek dine opgaver";              
$send_mail3 = mail($email, $subj, $content3, $fra);

$content4 = "Tjek din opgave";                
$send_mail4 = mail($email, $subj, $content4, $fra);


Regards
Peter