Outlook Express attachments

When a mail is sent from MS Outlook 2003 on one machine to Outlook Express 6 sp1 on another machine (both machines XP sp2, all updates installed), the user with Outlook Express does not receive the attachments. I have cleared the Do not allow attachments to be saved or opened that could potentially be a virus option and removed the check mark to allow the file extension to be downloaded, Does anyone have any other idea have the user can open the attachment?