Problem Sending email to users with lotus notes

We use outlook and exchange 2003. When our users send an email with an attachment to our home office in Japan, somtimes it arrives with out the original attachment. Instead it has a “$RFC822.eml” attachment wich just contains the original body of the email. Our home office in Japan utilizes domino and lotus notes. I am trying to determine if the problem is on my end or theirs. I have examined my exchange setup and can find nothing unusual. Anyone have any ideas?