1. Start a new message.
2. Click on the address book to the left of the TO:... field.
3. Find your departmental address list in the GAL (Global Address List) and select it.
4. Click on the TO: button.
5. Click OK. You can click on the + to expand the list if you need to remove individual names for a particular message.

Note: you must be a member of organization in order to send to departmental lists within that organization. (e.g. ORG=Finance & Operations, DEPT=Human Resources).