A Distribution List is a collection of contacts. If you frequently send messages to a certain group, you can create a distribution list that contains the addresses of all members of that group. A message sent to this distribution list goes to all recipients listed in it. Recipients see their own names and the names of all other recipients on the To line of the message instead of seeing the name of the distribution list.
Click on New, Distribution List. You will see a screen similar to the one below.

Type a name for the distribution list in the List Name field. Then add members to the group by e-mail address. Click Add. When your finished adding members click Save and Close.

To use your distribution list, simply type its name into the To line of a new e-mail message. The e-mail will be sent to all members of the list.

To make future changes to your list, Click Contacts and then double-click your distribution list.