I recently installed a 2010 Outlook Client from Office 2010 Home and Business and it is accessing a 2003 Exchange environment. I began to get this error on larger emails being sent out and then the email would delete from the sent box leaving this in the inbox Your message did not reach some or all of the intended recipients. Subject: FW: Sent: 4/14/2011 5:18 PM The following recipient(s) cannot be reached: xxxxx@xxxx,com on 4/14/2011 5:18 PM This message could not be sent. Try sending the message again later, or contact your network administrator. The client operation failed. Error is [0x80004005-0xfffff9bb-0x000501]. Any thoughts?