Attachments in Outlook to OE

Hi all, got a user using Outlook 97 (connected to an Exchange server) sending a simple Excel document to 9 others users who are connected to a mail server (not Exchange – Linux software) and use Outlook v5 and v6. The email is going through to the users, but 6 users haven’t received the attachment. I’ve checked the security settings on the receiving PC’s and also made sure that the senders PC is sending out in Exchange RTF format.

Anyone got any ideas?