Losing mails Between SendMail and exchange

[David Rocks]

I am hoping that someone could help me discover why my mail program using sendmail on solaris cannot seem to send mails to an exchange server. I can send mail to hotmail and other such addresses. It must be a flag that gets set in the message but i cannot work out what it is. This is the method that i use.
public synchronized void sendMessage( String sendTo , String subject , String contents , String from , String replyTo ) throws Exception {

// create a message
MimeMessage msg = new MimeMessage( session );
InternetAddress[] address = { new InternetAddress( sendTo ) };

msg.setRecipients( Message.RecipientType.TO, address );
msg.setFrom( new InternetAddress( from ) );
InternetAddress intAddressArray[] = { new InternetAddress( replyTo ) } ;
msg.setReplyTo( intAddressArray ) ;
msg.setSubject( subject );
msg.setSentDate( new Date() );

MimeBodyPart mbp1 = new MimeBodyPart();
mbp1.setText( contents );

// create the Multipart and its parts to it
Multipart mp = new MimeMultipart();
mp.addBodyPart(mbp1);

msg.setContent(mp);

// send
Transport.send(msg);
}
If anyone has even a small suggestion it would be much appreciated
Yours
David Raid