Creating a distribution list of outside e-mail addresses

You have two options:

1. Add a contact to your Active Directory for each of the external SMTP addresses, and then put them all in a distribution group.

2. Drag and drop all the contacts created in someone's mailbox (assuming they are already in someone's mailbox now), and move or copy them to a public folder created to contain contact items. Give everyone permissions to access this public folder, and then have them right-click the public folder in Outlook and select Properties → Outlook Address Book → Show this folder as an e-mail Address Book.

Test both options in a lab to determine which best meets your needs.

If I've used option number two, how would I get contacts in the public folder to list individually in Exchange? Right now my users can send mail to the public folder group as a whole, but not to individuals in the public folder.

Thanks in advance for your advice.
—Shirley M.

******************************************

If I understand your question correctly, you're saying that sending to the contacts as they appear in the new client-side Address Book fails.

If so, you'll want to navigate to Global Settings -> Internet Settings in Exchange System Manager (ESM). Then right-click "Default," switch to the Advanced tab, and ensure that the "Allow automatic forward" checkbox is set.
—David Sengupta, Server Administration Expert

Related information from SearchExchange.com: