Switch your view on that folder to an unfiltered table view, such as Phone
List.  Use CTRL+A to select all items in the folder.  Depending on your
Outlook version, you can right-click and select "New Message to Contact", or
click the Actions menu, then Create, then New Message to Contact.  All of the
primary e-mail addresses for those contacts will appear in the To field of
the new message.  However, for privacy's sake, you should move the addresses
to the BCC (blind carbon copy) field instead, and put your own address in the
To field.  Everyone will get your message but they won't see anyone else's
e-mail address (or their own for that matter).