Important: January 20, 2017: There's a known issue when sending email to a Contact Group results in error "An unexpected error has occurred" being displayed. We're working on fixing this issue. As a workaround, you can click the + icon to expand the Contact Group to send the email.
Use a contact group (formerly called a “distribution list”) to send an email message to multiple people—a project team, a committee, or even just a group of friends—without having to add each name each time you want to write them. To use an existing contact group:
Click Home > New Email.
In the new email message, click To.
Note: The Global Address Book is set as the default address book in Outlook. However, you can change the address book. To change the address book, under Address Book, click the down arrow and choose a different address book.
In the Search box, type the name of the contact group.
Double-click the name to add it to the To box, and then click OK.
Of course, contact groups don’t create themselves. For more information about how to create a contact group, see Create a contact group.