I'll assume you are using Microsoft Outlook. The following are some common reasons why new messages that you send do not leave the Outbox:
1. If you use offline folders or Remote Mail, you must use different commands to send and receive messages.
2. If you open a message in the Outbox, or edit it and then save changes, the message is not sent. Open the message, and then click Send.
3. If you are using Cached Exchange Mode, you might have chosen to work offline and have no send/receive group settings configured to periodically connect to the Microsoft Exchange Server. If you are working offline, the status bar will display Offline. To return all accounts in the profile online, on the File menu, click Work Offline . To only reconnect the Exchange Server e-mail account, on the File menu, click Connect to Microsoft Exchange Server.