If you are having problems sending an email to a certain person or to a distribution list like PBS All, HS Teachers, MS Teachers, etc, then you may need to clear your auto complete list in Outlook
...
using these steps:
Open Outlook and click "File" and then click "Options"
In the Outlook Options window that appears, make ensure that "Mail" is selected
inon the left
pane and in the right pane scroll to the Send Messages area.
- Click
-side of the window and then scroll down using the scroll-bar on the right-hand side of the window until you get to the "Send messages" area.
Click the "Empty Auto-Complete List" button and then click "Yes" in the dialog box that appears.
You have successfully cleared your Auto-Complete list now and it will begin to repopulate email addresses as you compose and send messages to people.