I want to take an inbox e-mail with multiple recipients and convert the collection to a GROUP in CONTACTS.
These are the steps I just took. I'm on a Mac with Lion 10.7.5 OS. I also tried this on Leopard. Sounds like a lot, but it's better than adding addresses one by one.
First, download and install mailscripts: https://www.macupdate.com/app/mac/9178/mail-scripts/
Once it's installed, you'll find it in the upper right menu bar looking like a scroll. Once you've done this, you won't have to do it again.
Create a new group in your address book.
Then create an email or forward an email and move your recipients into the "To" line.
Go to your drafts folder and highlight that new email with those address.
Now go up to your scripts in the menu bar. Select Mail Scripts > Add Addresses. Be paitent for a new window to appear. It should contain all the address from that highlighted email in your draft folder.
Check "select all." Choose the new group you created from the dropdown. Choose the email label from dropdown. Click "Add."
Voila, the names are in a group.