You may have learned the hard way that if you open a distribution list in Outlook 2007, highlight one contact, and click on Delete, the entire distribution list is deleted!
The trick is to click on Remove instead of Delete in the distribution list ribbon bar:
Tip: if you do accidentally delete the entire distribution list, check you Deleted Items folder. If you’ve already cleared your Deleted Items contact MCB Systems. We may be able to restore the distribution list from a backup.