The latter. Adding contacts to an address book is simple though. Just click the star to the right of the sender's email address in the message header. https://support.mozilla.org/en-US/questions/1077025

To create a mailing list see http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Create_Mailing_List

Thanks. I knew about the second method. Was hoping for something a bit faster.

Up until recently I would have suggested two add-ons to you:

More Functions For Address Book Email Address Crawler

The first will allow you to gather addressees from the currently selected message, and add them to an address book. The second will walk over multiple selected messages and collect addresses from the headers and the body text, and then add them to a List or address book.

Unfortunately, the author of both these ad-ons has stated he will not be re-writing them to make them compatible with the current implementation of Thunderbird. I mention them because they may still work for you.

If the data is presented in an orderly manner, in a table or organized into columns, you may find that you can select and copy the information, paste it into a spreadsheet or text editor where you can tidy it up, and then you may find that when it is organized as it would be in a CSV file, you can just copy-and-paste it into a new Mailing List. This will have the side effect of adding these addresses as new Contacts into the List's parent address book.

MoreFunctionsForAddressBook works in TB 60 if you first open Tools/Options/Advanced/General/Config. editor and double-click the preference extensions.strictCompatibility to false, OK to close Options.

The attached picture shows the menu when you right-click a recipient in the Message Header to add the recipients to a mailing list. You will be prompted to name the list and specify the target address book.

Worked like a charm! Thank you!!