It’s quite easy to inadvertently delete an entire distribution list within Outlook. Instead of selecting a single contact, you accidentally select a distribution list and click the Delete button. Unfortunately, a dialog box does not appear prompting you to confirm your actions.
If this happens to you, there is no need to panic because you can easily recover the distribution list. The deleted list is moved to the Deleted Items folder. As soon as you delete the list, go immediately to the Deleted Items folder, select the list and drag it to the Contacts folder.