A distribution list is a group mail, you can easily create a list and send them all messages at once.
You can create a distribution list for each team or department.
To add user to contacts group:
1) Open WorldPosta control panel.
2) Click on Mailboxes in Hosted Organization section.
3) in Mailboxes page, click on the user that you want to edit.
4) Click on the tab Member Of.
5) Click on Add in the section Groups a list of your groups will appear.
6) Select groups from the list, then click Add Accounts.
7) Click on Save Changes or Save Changes and Exit when you’re done.