Here is what Windows help tells you to do to create a group mailing list. However, it doesn't work for me since I don't see a toolbar in the contact list. Anybody else seeing a toolbar? Maybe these instructions were written for OE and they haven't updated for WM.
Create contact groups (mailing lists)
A contact group is a collection of contacts that simplifies the process of sending e-mail to groups of people. By addressing a message to a contact group, you save time by not having to add an address to the message for each recipient. You can send the message to everyone in the contact group at once.
When using contact groups, keep in mind that they do not hide the e-mail addresses of the recipients. When you send a message to a contact group, all the recipients will be able to see the names and e-mail addresses of the other recipients.
Contact groups are designed to be used with Windows Mail, and are sometimes called mailing lists.
1.. Click to open Windows Contacts..
2.. On the toolbar, click New Contact Group, type a name in the Group Name box, and then fill in the boxes on the Contact Group tab and Contact Group Details tab. You don't have to fill in all the boxes; just type as much information as you want about the new contact group you are creating.
3.. Add contacts to the contact group in any of the following ways:
a.. To add individual contacts to the group from your existing contacts, click Select Members.
b.. To create new contacts and add them to the contact group, click New Contact.
c.. To add new people to the contact group without also adding them to your individual contacts, type the appropriate information in the Contact Name and E-mail boxes, and then click Add.
Tip
a.. You can send an e-mail message to a contact group using Windows Mail. To do this, open Windows Contacts, right-click a contact group, point to Action, and then click Send e-mail. This will open a new e-mail message in Windows Mail addressed to all the members of that contact group.
See also
a.. Managing your contacts
b.. Add or delete contacts
c.. Organize and find contacts
d.. Working with Windows Mail
I believe it's possible for a recipient to see everyone who's on the BCC list by looking at message headers. So, that approach isn't as secure as you might think.
I've seen people create mailing lists that do what you want to do. But I don't know how to do that. (And I'm not talking about something like Yahoo Groups here. This is something else.)