attachment problem

Hi, since a couple of day we have a little problem. When we send and outside email with an attachment, people receive the attachment in code. We are on Exchange 5.5 with sp3.People receive the mail with this message: This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. The same problem occur when we send the email to hotmail or something like that.

Thanks

Yves Fortin