We experience a strange problem. Some mail with pdf, xls and/or xlsx attachments is not received by outlook. They appear in the Outlook inbox but the disappear. There are no rules activated! When we lookup these mail in OWA the mail has been transferred to the OWA folder Problems with synchronistation, server errors. So the mail is not visible in Outlook but is visible in OWA. It's not the extension because other mail with pdf, xls or xlsx does arrive without a problem. It's not the antivirissoftware because we have disabled that software.
The server is a SBS 2003, clients use Outlook 2003 and 2010. Both clients have the problem.