Regarding Microsoft Exchange server

When i am sending mail's it just keeping my mails in outbox. When i click ed the send/receive it showing the following error message

""Task ‘Microsoft Exchange Server’ reported error (0x8004011D): ‘The server is not available. Contact your administrator if this condition persists.’

Task ‘Microsoft Exchange Server-sending’ reported error (0x80040115): ‘The connection to the Microsoft Exchange Server is unavailable. Outlook must be online or connected to complete this action’ ""

can any one plese tell me what the problem is.....

i am using Microsoft Outlook 2003............

Thanks & Regards

[1426 byte] By [sree1030] at [2008-1-9]