Try looking at these options for a solution....
I received an "Undeliverable" message notification from the administrator.
The server might be busy or offline temporarily. Wait and then try sending
your message again.
How?
In your Inbox, open the "Undeliverable" message.
On the Actions menu, click Send Again.
In the message, on the File menu, click Send.
If you are using Microsoft Exchange Server, check to see if your name exists
on the server.
How?
On the Tools menu, click E-mail Accounts.
Select View or change existing e-mail accounts, and then click Next.
Click the e-mail account you want to change, and then click Change.
Click Check Name. Your name and server should become underlined. If not,
contact your administrator.
When creating your account, you might have typed an incorrect user name,
password, or e-mail server name. View your e-mail account settings to see if
they are correct.
How?
On the Tools menu, click E-mail Accounts.
Select View or change existing e-mail accounts, and then click Next.
Click the e-mail account you want to change, and then click Change.
Make sure that the settings you see match the information you received from
your Internet service provider (ISP) (ISP: A business that provides access to
the Internet for such things as electronic mail, chat rooms, or use of the
World Wide Web. Some ISPs are multinational, offering access in many
locations, while others are limited to a specific region.) or administrator.
If necessary, make your changes in the appropriate boxes. If you want to
change additional settings, click More Settings. Otherwise, click Next.
Click Finish.
