I have Exchange set to defaults so allowing send and receive limits of 10MB and AD users set to default limits. I have users that are able to received 6mb size emails, but anything over this limit the email seems to disappear into thin air. It only appears to be emails with large attachments. I can see the email coming through the firewall then does not land in the inbox. There are no undeliverable messages sent to the sender? Where can I look now?