Macro to Reply All in Outlook

This has nothing to do with Excel. You would use VBA in Outlook if you were to do this.

If you are in Outlook 2010 I believe it has a quick parts area at the top on the Home tab. You can create a "template" of sorts with this to reply/reply all. Not sure if it can be used beyond a single message at a time, but I would start with that.

Also depending on how many messages this is, you may not be able to reply all on them all at the same time. Many companies and services limit the outgoing messages per/time period to prevent spammers from mass mailing. Just imagine if you have "only" 100 messages in the folder and each message had 20 recipients. Thats 2000 outgoing emails at 1 time. You could potentially via a macro set it to send x emails then wait y time before sending another x emails....at that rate your Outlooks tied up by your macro and you cant use it while it does this.

That doesnt even take into account having a recipient in many emails. If you had 10 emails in that folder with/from me on it and did what your thinking, id get 10 emails and be pretty mad about it.

Maybe a better approach, depending if all these emails are closely related enough (as you seem to want to reply to them all with the same template any way) is to instead get a list of all the unique recipients from all the messages and send 1 email to the recipients. Still alot of messages but this way they all only get 1 reply and you still address all the emails in that folder in a fashion.