Does the attachment problem affect only some users? So can some users send attachments with no problems? If that is the case then you might want to check the user permissions (mail directory) on the mail server.
HTH, Nitin
Fresh Postfix/Cyrus OS X server, all the permissions are cyrus as needed and valid. Sending attachments is not an issue, viewing ones that are sent is -- it seems to be microsoft office related. I have half a mind to just clear it out and do a fresh installation...