After successfully sending an email message with Outlook 2007, when viewing your mailbox in Outlook Web Access, the message is located in the
Outboxfolder indicating the message is waiting to be sent. This is caused by a known Microsoft issue with Outlook 2007 and Outlook Web Access. The issue is fixed in a Microsoft hotfix dated February 7, 2008.
To resolve the issue, apply the Microsoft Hotfix Package for Outlook 2007. For more information on the hotfix, see the following Microsoft Support Site articles.