When I receive an attachment in an email, the file is converted to
Any ideas why, and what do to avoid this happening?
The person sending the e-mails is using an Exchange Windows or Outlook client. If your e-mail client does not support Rich Text Format (RTF) you will see this as a binary file attachment. It contains Microsoft Exchange Server RTF information.
On your side there is not much you can do unless your client is programmable and you can filter out certain attachments. This particular issue is usually resolved from the sender's side.