Windows Live Mail lets you create contact categories to organize your address book into groups of related people: this feature is more widely known as "contact group", "contact list" or "distribution list", and lets you easily send mass emails just by typing the group name as recipient (e.g., "sales team
"). This tutorial explains how to create a new list, add/remove contacts from it, and email it. Another explains how to rename, delete, or add new members to a contact category.
Note: grouped contact lists do not create any duplicate entries in your address book. A distribution list only contains references to the individual people you add to it. The same person can belong to multiple groups, and his/her name or email address is automatically be updated if you change that contact's information.
First, go to your Contacts: hit Ctrl+3 or click the address book icon 
(bottom left).
Click on the Category button in the ribbon.
When Windows Live Mail opens the "Create a new category
" dialog, type a meaningful list name in the first text field: something that, in a few months, will still let you guess what contacts are in it!
The middle portion of that window shows an alphabetical listing of all your contacts: click on any of them to add them to the group. Click on a selected one again to remove it. Corresponding email addresses are added to the text box at the very bottom as you populate your list. Notice that you can resize the address box: 
Tip: you can also type an email address in the text box at the bottom, thus adding to your list even people not currently in your address book!
When you are done, click "Save" - your contact category is ready!
Let's now test your category by sending a group message. Its name behaves just like your contacts' names do: as you start typing in one of the recipient fields of a message window, Windows Live Mail will auto-complete suggestions. Enter your distribution list name as recipient, and all people members of that group will receive that email! 
Caveat: while Windows Live Mail only shows the category name as recipient when you compose the message, it will show everybody's email address when the group message is delivered. To send a private mass mailing list (with hidden, "secret" recipients), type the group name in the Blind-carbon copy field:
To remove the category members from the mailing list, just erase their name from the To/Cc/Bcc field, like you would with standard email addresses. You can distinguish distribution lists from regular contacts by the "+" blue plus sign in front of their name.
Tip: click on the plus sign to convert the category name into a list of email addresses; hit Ctrl+Z several times to undo. This lets you to remove some recipients from the email, without removing them from the contact list itself!
