I wanted to reply to a bunch of emails. Contacts not in my address book. Didn't really want them in my address book. Easiest way I found...

1) Drag all the emails into a new folder in Mail (either highlight all using ctrl or drag individually)
2) Go to "File" Import Export
3) Export to file, select your new folder
4) Export to comma seperated excel file
5) Highlight and copy all the email addresses on the excel sheet
6) In Outlook, go to "File" New distribution list
7) Go to "Select Members"
8) Paste the email addresses from your excel file into 'members' field at bottom